US2470578A - Thermal molecular alteration of carbon compounds - Google Patents

Description

May 17, 1949.

THERMAL MoLEcULAR ALTERATIQN voF -ARBoN coMPUNns Filed oct. 3, 1942 P. H. ROYSTER 4 sheets-sheet 1 May 17, 1949- P. H. RoYsTER 2,470,578

THERMAL MOLECULA ALTERATION OF CARBON COMPOUNDS Filed Oct. 3, 1942 4 Sheets-Sheet 2 May 17, 1949. P. H. RoYsTER 2,470,578A

THEMAL MOLECULAR ALTERATION OF CARBON COMPOUNDS Filed Oct. 3, 1942 4 Sheets-$11661: 3

3mm/bola.'

PMLH'. Rhys@ May 17, 1949. P. H. RoYs'rER 2,470,578A

THERMAL MOLECULAR ALTERATION 0F CARBON COMPOUNDS Filed oct. s, 1942n 4 Sheets-Sheet 4 Patented May 17, 1949 UNITED STATES THERMAL MOLECULAR ALTERA'IIION'OF CARBON COMPOUNDS Percy H. Royster, Bethesda, Md.

Application-October 3, 1942, Serial No.f460,658

3 Claims. 1

'This inventionV relates `tothe artof thermally altering the molecular constitution of carbon compounds and is concerned withirnprovements in such processes `and with apparatus vadapted for -use in `the vcarrying yout of such improved processes. limprovements inthe cracking of hydrocarbon oils such, for linstance, as crude petroleum, gas-oil,

Thus, the yinvention contemplates fuel oil, kerosene, or'petroleum residues, whereby vto produce hydrocarbon oils such, for instance, as y,gasoline or ,gasoline-containing cracked distillates, having lower molecular weights and/or lowerboiling'points than the starting materials.

It specifically contemplatesv a process for the commercial production of ya lower boiling product such as motor fuel and in particular a low yboiling point motor fuel exhibiting 'high anti- `knock properties. :alsoa treatment of hydrocarbon gases such as The invention contemplates natural gas, methane, ethane, ethylene, propane,

landlthe like, and mixtures thereof, particularly non-condensable gases formed in cracking .petroleum lin present renery practice, whereby to form hydrocarbons of `higher boiling points than the starting materials. Further, it contemplates improvements in processes of thermally treating-hydrocarbonsof any molecular weight Vwhereby to effect alchange in molecular constitutionrby such thermal means, in the presence ,or'absence of catalysts, as well as to subjecting the; hydrocarbons to thermal and chemical treat- 4ments wherein reactionsinvolving oxidation, re-

duction, `hydrogenation, hydration, dehydration, andthe like, may takeplace.

:An object ofthe present invention is the pro `vision of an improved `themal process whereby reactions may be carried'out more eiiiciently at .elevatedltemperatures and at pressures varying `from commercial vacua to the upper extremes of :high pressures` Another object of the invention is. the provision of an improved process for the production of modern anti-knock motor fuel from ,crude petroleum, distillery intermediates, and

residues. The provision of an improved. process for vthe hydrogenation under suitable pressures of Iless marketable renery products is another objective. An improvement in the so-called reforming of naturalgas, methane, ethane, or the like, with steam to form hydrogen and carbon monoxide is still another objective,

In general-it is the object of this invention to vprovide an improved method by which a thermally unstable uid may be subjected 4to a `thermal treatment at a carefully controlled sage thereof through the heated jmass,

2 temperature. for ,a .cnnlllQIlQCl P91210@ 9i.' whereby to produce ga Lsubstantialamount-qi a second fluid, which `itselfis lunstable ,at lthie -thermal treatment temperature, rWthQllt gconcurrent material thermal destruction :pffsaid second fluid. Included aaniongf thelobiectsj of invention ,is Athe provision,,offappallliuspeculiarly adapted for use in carrying!loutifcracking and Similar thermal..treatmentpmeseeewhie D.-

.paratus vmay be .constructed :mere {cheaply-,than

The general process of the present ;i;tvention isas follows: v .thlQllhf-.the ntersticesrof; almass of heatfabsorbns @articles lenelesed @infra carrier gas heated to an elevated gtenipcigature T2 (T2 beine at least llecual its :the @alteration temperature) ,rt-he passage of zthe l'httdirllil eas being continued runtil :an appropriate itemnerature 'distribution 112sy established; in vthe. :mass:

thereafter, :a stream of the fuid to :he :treated ,at a temperature 'Ilo,.1(i. ie., ahelowtthermalratklthis process, control -of the rate fof ilovv for` the fluid vto'fbe treated throughlthe' mass ofxheaited particles `prefer-ably 'is so 1 'determined with *11espect Kto the lvolume, 1density,"-spalcedistributibn of temperaturefand-shapegof saidmassth teach part or portion'oflthestreamggf'nuidfis byfpasto the desired thermal `alterati'on"'temp ytigre and l not lmaterially 4thereoverffmdfis maintained thereat for l the proper time interval '.ofthermal alteration.

It is affeaturefof thisdnVention jthatftheas semblage of Lheat,exchangingV solid particles 'l is .so designed AAto makes-possible 'if'sochroneus flow vof the.strea,m.fof ,luid-therethrougfhfby which latter expressionsajmeanithateach portion of the fluidfstreamrremanszln. heateexchcnging contact with the` heat-exchanging soldlarticles for the same period of effective time. A unit of effective time at any given temperature lower than T1 is defined as the length of time in which the same reaction takes place in one second at T1. When this special type of uniformity of uid flow (i. e., isochronous flow) is realized, the proper interval of heat-exchanging contact between the stream of fluid and the pre-heated solid particle mass is' readily attained and maintained by appropriately controlling the rate of flow of the total stream of fluid; if the effluent product is found to contain excessive amounts of decomposition products of the altered substance, time of contact has been too long and, to correct this fault, the rate of fluid ow is increased; if the content of altered substance in the eiiiuent product is found to have diminished, the time of contact has been too brief and accordingly the rate of fluid flow is diminished. Such a method of control can only be attained satisfactorily where the time intervals of passage of the several portions of the stream of fluid are substantially the same; that is, when the-paths are isochronous or substantially so.

The invention will be described in greater detail in the following illustrative but not restrictive examples, taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic showing of an apparatus for carrying outa process embodiment of the invention;

Fig. 2 is a graph illustrative of temperature distributions within a reaction chamber of the `apparatus of Fig. 1 during the carrying out of the process;

Fig. 3 is a diagrammatic showing of a modied apparatus for carrying out a modified process in accordance with this invention;

Fig. 4f is a graph illustrative of temperature distributions within a reaction chamber of the apparatus of Fig. 3 during the carrying out of the modied process; and

Figs. 5 and 6 are diagrammatic showings of further modied apparatus in accordance with this invention.

An embodiment of the present invention from the standpoints both of process and of apparatus will now be Idescribed with reference to Figs. 1 and`2.A ,i

In Fig. ,1,J the. reference numeral I represents any suitable oil supply container, 2 represents a variable-speed oil pump, 3 represents a suitable heat-exchanger of the tube type, and 4 represents a, suitable pipe heater, these four pieces of apparatus being connected in the order named by suitableconduits provided with suitable valves. 5 represents a manifold conduit connecting pipe heater 4 with-each of the three similar reaction chambers A, B and C through suitable oil vapor inlet valves 6a, 6b, and 6c, respectively. Each of reaction-chambers A, B and C is a thermallyinsulated, gas-tight vessel provided with suitable openings: in each is `an open space (illustrated in chamber A at la.) at the bottom, above which are suitable grates or other supports (3d in cham- ,"ber A) upon which is supported a mass of promiscuously deposited, relatively small, solid heat-exchange bodies, e. g., pebbles (9a. in chamber A),'above which massis an open space (10a in Vchamber A). Chambers A,'B and C may be so designed that the aforesaid masses of heatexchange solids are relatively broad for their height-e. g., even broader than high-where low pressure drop is a technical desideratum.

In appropriate openings adjacent the tops of chambers A, B and C and in communication with their upper open spaces (10a in chamber A) are arranged appropriate branches of manifold conduit il controlled by the valves ila, Ilb and llc, respectively, which conduit l l communicates with the interior of heat-exchanger 3. l2 represents a suitable cooler, connected by suitable piping with heat-exchanger 3 and with product storage tank i3.

The reference numeral i4 represents a steam line, in communication with a source of steam (not shown), with branches Illa., |41) and 14e, controlled by valves ld, |511 and 15e, respectively, in communication respectively with the upper open spaces I0 (lila in chamber A) of chambers A, B and C.

The reference numeral l5 represents a suitable air heater into which air under pressure can be forced by blower I6 connected thereto. From air heater l5 extends manifold conduit l1 with branches lla, Ilb and llc, controlled by valves 18a, ISb and |80, respectively, in communication with the upper open spaces l0 (Illa in chamber A) of chambers A, B and C, respectively.

From the lower open spaces (la of chamber A) of chambers A, B and C extend conduits 19a, IBb and |90, controlled, respectively, by valves 20a., 20h and 20c, which conduits ISa, 19h and 19C either discharge into a chimney (not shown) or directly into the atmosphere.

As a definite illustration, a crude petroleum (38 A. P. I., 300 lbs/bbl.) with an initial boiling point of 207 F., distilling a 23% naphtha fraction below 337 F. and a 35% crude kerosene fraction between 337 and 572 F., is forced by oil pump 2, at the rate of 73 bbls./min. through heat exchanger 3 and thence through pipe heater 4 in which it is heated to 700 F., i. e. below cracking temperature. The so preheated oil flows from pipe-heater ll through conduit 5 and open oil vapor inlet valve 6a and enters open space 1a below grate bars 23a and thence passes upwardly through a mass of superimposed pebbles 9a. Pebble mass 9a is cylindrical, 24 ft. 9 inches in diameter, and has an axial dimension of 15 ft. Its volume is 7,350 cu. ft. This mass, consisting of pebles screened between l" and 11/2, weighs 109 lbs. per cu. it., and shows a 38.8% volume of voids. The total weight of 9a in chamber A is 800,000 lbs. At the beginning of the described operation these pebbles are heated at the substantially uniform temperature 1000 F., i. e., at cracking temperature.

The actual flow of preheated petroleum vapor, as it enters pebble-mass Qa is 83,000 cuit/min., measured at entrant conditions (13 cm. Hg gauge pressure, '700 F.) for an oil having an average molecular weight of 190. Hence the mean upward velocity of vapor through the interstices between the pebbles is 7.45 ft./sec. rihe time of transit through pebble mass 0a would be 2.00 seconds were the specific volume of the fluid unchanged during transit; however, its specific volume is changed in the following respects: The temperature of the petroleum vapor increases in passage through mass 9a from 700 to 1000" F. whereby its volume is increased 25 per cent. With reduction in the mean molecular weight from for the vapor before treatment to 142 for the vapor after treatment, the vapor volume is increased a further 25 per cent due to the cracking reaction. Assuming an irreducible minimum decomposition of cracked product during formation suiiicient to form 2% solid carbon, and a simultaneous production of 2.6% by weight of Xed gases, the vapor volume is increased 55 per cent from this cause. The decrease in pressure experienced by they stream in transit causes an increase of only 17%. The total eiect of these four causes, temperature-rise, molecular change, formation of xed gases, and drop in pressure, is to increase the rate of flow of petroleum by volume from 83,000 cu. ft./min. at the point of entrancey into pebble mass @a to about 197,000 cu. ft./min. at the point of leaving the same. The velocity of the fluid stream is 13.6 ft./seo. at the top of pebble mass 0a compared with 7.3 ft./sec. at the bottom of theI mass. The average velocity for the whole path is 10.5 ft./sec., and the time required for the fluid to traverse pebble mass 9a` is 1.42 seconds, including the time consumed by the Vapor in passing through space Ita and manifold conduit I I. Where the crude petroleum stock used for this illustration exhibits characteristics similar to the Grosny crude used by Sachanov and Tilicheev Petroleum, vol. 23, page 521, 1927), the rate of production of motor fuel is 45.4% per second at 1000" F. Since the mean yield of cracked product in the experiments of Sachanov and Tilicheev was 64.5%, it is seen that the iiow of 73 bbls/mm. permits completion of the cracking reaction to take place just as the iiuid completes its transit through pebble mass 9a. The vaporous product emanating from pebble mass 9a rises into open space Ita above said mass and passes from reaction chamber A into conduit II and thence through heat exchanger 3 and into cooler I2 and is cooled to below thermal alteration temperature immediately after the completion of the reaction; thereby over-cracking (due to too long exposure to high temperature) is largely avoided. In heat exchanger 3 the vaporous product indirectly imparts heat to the incoming crude petroleum.

The operation takes place as described above only at the beginning of the passage of the iluid stream through pebble mass 9a. Petroleum vapor at the rate oi 21,900 lbs/min. enters pebble mass 9a, at 700 F. Each pound of oil requires 216 B. t. u. to raise its temperature from 700 to 1000 F. Hence 4,740,000 B. t. u./min. are transferred from pebble mass Sa to the uid stream and the pebbles themselves are cooled to 700 F. When 129 barrels of crude petroleum (129 barrels throughput) have been forced into reaction chamber A (a stage in operation designated epoch I) the temperature distribution in pebble mass i3d is as shown in curve' a of Fig. 2, in which the vertical distance above the grids 8a (designated fc) is plotted as abscissae and temperature (in degrees Fahrenheit) is plotted as ordinates. In heating 129 barrels of oil from 700 F. to l000 F., 61,000,000 B. t. u. is removed from the pebbles in the lower part of mass 9a, a quantity of heat represented in Fig. 2 by the area between curve a and the 10G-0 isotherm. At Epoch I, the mean temperature of 9a is less than at the beginning of the operation and it is obvious that insufficient time of contact would be permitted to realize the completion of the cracking reaction if the ilow rate of 73 bbls./min. were maintained. This flow rate is therefore continuously diminished at a controlled rate from the begining of the operation and when epoch I has been reached is reduced to 34 bbls/min., which permits the oil vapor in transit to remain in pebble mass 9a for gure upwardly in the aparatus) 3.75 feetl and ir l 8x.

for curve b is less than forcurve a. The maximum temperature gradientror curve bis 48 F. per foot and for curve a, is 67 F. per foot. The luid flow is continuously` diminished after epoch I and at the end of epoch II vit has been reduced to 17.4 barrels/min. to permit completion of the cracking reaction Within pebble mass 9a. and open space 50a. At 515 barrels throughput (epoch III) temperature distribution in 9a is` given as curve c in Fig. 2. The appropriate oil flow at Epoch III is 10 bbls./min. At this point the cracking operation is preferably terminated. The isothermal region at 1000 F., which was. present from the beginning through epochs I and II, has practically vanished at epoch III, and further immediate operation in reaction chamber A is unproltable.

From the beginning of the operation to the end of epoch III, the rate of oil ow-was diminished continuously from an initialV maximum flow of '73 bbls/min. to the nal minimum of 10 bbls./min. The rate of ilow of the fluid at each intermediate epoch Was adjusted in relation to the temperature at each portion of pebble mass 9a and the length of time each portion of the iiuid remained at each such temperature was so controlled that the cracking reaction reached completion just as the vaporous product completed its passage through ta, lila and I I. In this way over-treatment and under-treatment` are both avoided.

The previously described operation in chamber A is termed on stream.

Reaction chamber A is then taken off stream and the cracking process terminated at epoch III. Valves 0a and I la, Fig. 1, are closed. Steam from steamdine M through opened steam-valve Ia traverses chamber A downwardly from open space lila to open space 'Ia sweepingl residual petroleum from mass 9a, and discharges through opened purge valve 2Ia which, with purge valves 2lb and 21C, connects (through suitable conduit not shown) with cooler 22, in which latter both petroleum and the steam are condensed, the petroleum separated from the condensed steam being collected in purge collector 23 for further use. Concurrent with the above purging step in chamber A, reaction chamber B, already heated to 10000 F., is placed on stream and the operation described above for chamber A is repeated for chamber B, valves 6b and IIb-beingopened.

When petroleum vapor has vbeen purged from chamber A by steam, any suitable carrier gas preheated just above 1000 F. inA agas heater I5, is forced by blower I6 into the top of chamber .A via hot-gas line Il and open hot-gas-valve |80. and passes downwardly through pebble mass ,9a and dis-charges through open-space 'Ia and open exhaust valve 20a to the chimney (not shown). This carri-er gas may readily be air, gaseous products of combustion, steam, or other suitable gaseous uid. The step of forcing hotY gas downwardly through the reaction-chamber is termed an on heat period.

Each of chambers A, B and C', whenon heat. sustains a flow of about 213,000-cu; ft./min. orair (measured at 60 FT), the capacity of blower I6 and of preheater I being, of course, about 426,000 cu. ft./min. Continuous operation is maintained with this three-chamber plant; each of the chambers A, B and C is being subjected to the cracking step (on stream) for 20 minutes, and on heat for 40 minutes, following each other in repetitive alternating succession. The capacity of this particular illustrative plant is 37,000 bbls./day of feed-stock treated or 23,000 barrels of motor-fuel produced.

lIhe operation described above is used as an illustration of a manner in which the present invention can be carried out in a simple way.

The process of the present invention, it will be seen, is characterized by, among others, the following features:

1. The process is intermittent, and is carried out in two main steps.

2. In one step, heat is introduced into the uid to be thermally altered by heat-exchanging contact with a mass of solids, and, in another step, the solids are themselves heated.

3. The rate of ow of the fluid undergoing thermal treatment is varied during the on stream step, the iiow being controlled with respect to changing temperature distribution in the body of solids so as to bring to pass substantial completion of the thermal alteration of the fluid without material over-treatment of the latter.

4. The product formed is unstable at the temperature of formation and would be susceptible to thermal destruction were it permitted to remain heated at or near the temperature of formation for any material.

5. Each portion or element of the fluid to be thermally altered is heated at above a minimum and below a maximum temperature, for a period of time having determinable minimum and maximum limits.

6. Since the temperature distribution in the heat-exchanging mass of solids alters during on stream, the rate of flow of the fluid through the mass is varied to conform with the variation in the rate of reaction caused by this variation in temperature.

Although the inventive embodiment of illustration I is workable and technically successful, it has some possible shortcomings which can be avoided by practicing the teachings of the following speciiic example. It should be understood that the procedure described above in Illustration I and the accompanying Figures 1 and 2 has been presented for the purpose of describing, in a simple fashion, the thermal reactions which take place when an unstable uid is forced through a bed of pebbles, and neither the procedure nor the apparatus shown in Figures 1 and 2 is definitive of the present invention.

Illustration II In Fig. 3, oil from supply tank I is forced by pump 2 through opened valve 50a, into open space 5Ia, in reaction chamber 52a, through grate-bars 53a, into pebble-bed 50a; vertically through 54d into open space 55a; through conduit or crossover 56 into open space 55h; downwardly through pebble-bed 54h into open space 51h, discharging through pipe E'Ib, opened valve 86h, cooler 88, opened valve 581), into product tank 59. Gases not condensed in passage through 54h and cooler 88, escape through vent 90, opened valve 81 and separator 62 into a gas holder (not shown) The fluid flow described is termed direct stream and alternates with the following ow termed reverse stream. All valves are closed. Oil from tank I through pump 2 is forced through opened valve 50h, upwardly through chamber 52h, into open space 55h; through 56 into 55a; and downwardly through 54a, discharging through 51a, opened valve 86a, cooler 38 and opened valve 58h into tank 59. Pebble beds 54a and 54h are of identical dimension, 42 feet in diameter and 15 feet deep. The pebbles are similar to those in Illustration I.

Fig. 4 is a diagram with degrees Fahrenheit as ordinates and and as abscissae, where is the distance in feet in 54a measured upwardly from 53a (=0) Distance in 54a measured upwardly from 53a, is plotted in the diagram from left to right. The distance between the lines MM and NN in Fig. 4 represents the equivalent length of bed 55a, 56, and 55h, i.e., time of transit of fluid from top of 54a to top of 54h is the same as time of fluid transit through 4.321 feet of bed 54a or of Elib. In Fig. 4, x represents the distance in feet in 54h measured upwardly above 53h and is plotted from right to left.

The rst step (preliminary heating) of the process is: all valves are closed except a, 85h, 19a, 19h and Sla. Fuel from line 68 mixes with air from blower t5 in burners 18a and 18h, burns in 55a, 55D and 58, products of combustion discharging through Sa, Ela and chimney valve BIa. This combustion is controlled to heat 55a, 55h, and 5t to a selected reaction temperature, say 982 F. Blower G5 supplies 137,000 cu. it. air per minute to each burner. Fuel feed is controlled to maintain 55a at 982 F. Preliminary heating as described is continued for one hour and fortyve minutes, when the temperature in 54a is as shown in curve a, in Fig. 4. Valve Bla is then closed and valve Glb opened. Combustion prod-y ucts now pass downwardly through 54h for thirty minutes, when the temperature in 5417 is as shown by curve a in the right hand of the diagram in Fig. 4. Curve a. indicates the temperature in 56. All valves are then closed. The apparatus is then placed on a direct stream. Crude oil of Illustration I is pumped at the initial rate of 182 bbls./min. The oil fills open space 5 Ia, rises into contact with pebbles in Sila and is heated until at the temperature, T=207 F. initial boiling occurs. As the oil reaches higher levels in 54a it is heated, vaporized and superheated, exhausting into 55a at 982 C. The vapors pass through 56 into 54h and start down through 541). The superheated and almost completely cracked vapors are cooled down in traversing 54h, temperature of the passing fluid differing little at each level from the temperature of the pebbles at that level. During cooling the cracking reaction is completed and a cooled and completely cracked but not overheated condensed product trickles down through the lower levels of 54h, iiowing into product tank 59. Fluid in the transit described is subjected (a) to 7.3% cracking in the lov/er three feet of bed 5ta, termed front wave cracking (b) to 86.2% from .r=3 ft. to =II ft., termed crest cracking; and (c) to 6.5% from :c=11 to :c'=9, called back wave cracking. This direct stream step is terminated after twenty minutes (epoch I) during which 3620 barrels of feed stock are pumped into open space 5Ia and 2490 barrels of product discharge into product tank 59. Direct stream is terminated at this time (epoch I). Temperatures in the chambers at epoch I are shown by com- Vbeen transferred from 54a to the streaming fluid and carried into chamber 52h. This heat is represented by the areabetween curves a and b. Heat .carried through 56 into `52h was retained .in .54h .and .is represented 4by the .area between \curve b and a" vof Fig. 4,'i. e., 350,000,000 B. t..u.

.After epoch I all valves are closed; vand valves 94a, 86a, and 53a are opened. .Steam isladrnitted through 94a, and 1230 barrels of uncracked feed stock are drained into tank l. Valve BBaiis closed and valve 85h opened; steam from 94a sweeps through 55a, 56, 55h and 54h, hastening the draining of oil through the bottom of vlill) to tank "59. All valves are then closed. .The .above procedure is termed purging It is understood that -a purging operation between direct .and .reverse stream is optional with the operator, and although frequently desirable, cannot be considered Aa necessary feature of the process.

Reverse rstream is initiated, pump 2 Lforcing feed stock at an initial rate of 174 bbls/min. i-nto the reaction chamber 52h. After nineteen minutes (epoch II), during which 3300 barrels of feed stock enter 52h and 2250v barrels of .heated `ilud exhaust .from .52a into product tank 59., the temperature of 54a, 56 and 54h is as shownby curves c, c and c" in Fig. 4, respectively. y.During reverse stream '327,000,000 B. t. u. are removed from 54h (represented by the-areabetween b and and 94.65% .of `this heat (310,000,000

B. t. u.) is yreturned to bed-54a. This quantity-of heat is rep-resented by the area 4between the curves c and b in the left .diagram of Fig. 4.

Direct-stream and reverse-stream .together complete a cycle in which .a thermal distribution or temperature Wave (curves a, a' and a) has been moved up in 54a down in 54h, during direct stream to the position shown by-curves b, b' and b, and then returned during reverse stream to position identified by compound curve c, `c' c. 'Ihe value of (cH/(Z113)2 at epoch II is less at veach congruent point than at the beginning. By the thermodynamically irreversible transfer of heat, entropy has been generated, the temperature Wave has been spread out, the cycle vis not closed and the final thermal Wave (epoch II) differs in shape from initial shape a, a', a".. As the cycle is repeated the spreading out of the Wave continues and it is necessary continually to decrease the rate of iiuid flow to conform the time-temperature history of the fluid under .treatment to the rate of the cracking-reaction to permit the reaction to just reach completion during transit. For example, in this illustration 4600 .barrels are treated in the rst cycle (by cycle .is meant the combination of a direct stream step plus a reverse stream step, including whatever purging operations may optionally be employed) in 39 minutes; 4100 barrels for the second cycle in 42 minutes; and 3600 barrels in 45 minutes for the third cycle, etc.

Ultimately, as the temperature Waves in 5M, and 54h degenerate thermodynamically, the permissible flows of liuid Will decrease, until Aa completely degenerate state is reached. In Illustration II, operation might continue at a greatly decreased rate of flow until the temperature distribution (represented by curves d, d', d") is reached. Frequently this is undesirable. After 6 cycles of the above described operation, when 20,300 bbls. `of treated oil has been recovered in tank 59, oil is purged from the fluid circuit with steam, andan on heat step resorted to, where- 'after the 'operation described is repeated,

Fundamentally the operations described "in Illustrations I andII do not differ from each other. In Illustrations Iiheat for treatment was introduced into the fluid to be treated by heat-exchanging contact With solids preheated in a manner adapted to subject the fluid in transit to a time-temperature .history which caused the 4desired reaction to reach completion without subjecting the treated fluid to over-treatrnen and then the fluid was .cooled to quench the reaction by a Well-known 'type of cooler. To ele'ct this result rapid changes in the rate of `iluid ilow were necessary. In Illustration II the 'fluid tobe treated washeated as in Illustration I, and also was cooled after reaction to 'prevent 'overtreatment. The use of 'two reaction chambers in series to effect vboth the heating and the cooling .of the '.fluid to a great extent reduced the necessary variations in rate of flow. In addition, alarge recovery of lheat Was e1lected,'resullt ing .in marked improvement in the thermal elciency ofthe process. It is true, of 'course,'that interchanger 3 of Illustration I might be designedto attain an eiciency equal to that `real- `ized. in Illustration II but such an .interchanger is prohibitively expensive. For this reason "the attainment of high efficiency by the useof'a pair of reaction chambers in series is a deniteimprovenientI in the technology of the process.

Illustration III described until the temperature distribution is asrepresented by curves d, d', d" (Fig. 4). Op-

eration of direct-stream reverse stream is continued, .and the heat .necessary to maintain .satisfactory operation is introduced into cross- .over 56 vin the form of a heated carrier gas,

which conveniently .may be a controlled amount of vsteampreheated .in stoves 12a and 12b and `introd-uced into .56 through hot carrier igas lconduit and nozzles 96. Steam enters '55 at 1500" and rapidly and turbulently 'mixes with the .fluid stream there. .In the `particular lexample .given the amount of steam required is 6000 lbs/min.

At the initiation .of the operation, beds 12a and 12b are cold. They are operated alternately ,on gas and on steam. When 'I'Za'is on-gas fuel from 68 through open valve 66a enters burner .96a commingling with .air from blower 65 'entering through open valve 91a. Hot combustion products formed in open space 10a lpass downwardly through the pebble bed 'Ha ldischarging through open valve 84a to chimney. Fuel and lair to-96a are controlled to heat the top'oiflbed 11a .tolabove l500 F.

When va desired upper portion of 1Ia yis thus heated, all valves are closed. Valve 93a `is `opened uandrstearn .from .supply line 92 is introduced 'into stove 12a at the bottom, passes upwardly to vvatmosphere through opened valve v980i until prducts of combustion `are purged from 12a. Valve 98a is then closed, and valve 91a is opened, and steam from 92 passes upwardly through 12a, is heated substantially to 1500" F. therein and "discharges through 9|a, conduit 95, nozzles 96 ,into 56.

The alternate on gas and on steam steps above described for 12a are carried Aout identi- A'7&5 cally Ain '12b reciprocally to provide a continuous supply of steam at 1500 F. in 50 in controlled amount.

Illustration IV The equipment shown in Fig. 5 is useful in carrying out the present invention in the following manner. Four chambers are provided, lili, |02, |03 and |04, having in horizontal section the relative shape represented by the rectangular inside dimensions: 18 ft. by 50 ft., 20 ft. by 65 ft., 20 ft. by 65 ft., and 19 ft. by 55 ft., respectively. Chamber contains 1,960,000 lbs. of pebbles screened through 11/2 on l, resting on top of 250,000 lbs. of larger pebbles |00 of threeinch average diameter. Eight 4 ft. by 4 ft. arched brick conduits |01 connect |0| with |02. Chambers |02 and |03 each contains 2,500,000 lbs. of pebbles, largely of the 3 inch size forming beds |08 and |l2, respectively. Pebbles from |00 and |08 spill partly into |01, exposing free surfaces at their angle of repose and leaving an open space above. Wall I3| is provided with ten 4 ft. X 3 ft. arched openings I0 between open spaces |09 and respectively. The right hand wall of |03 has seven 50 inch circular openings I3 connecting with conduits H4 leading to open space ||5 of chamber |04. Chamber |04 encloses 3,200,000 lbs. of 1 inch-11A inch pebbles (bed H0) carried on pebble bed |33, 450,000 lbs. of three-inch particles. l

|04 contains' The lower portion of chamber arched constrictions |30 supported by arches |30 which provide the louver openings 1, H1. Inlet |31 connects blower |32 with and |1 when valve |38 is open. Air from |32 passes along u |39 through open valve |40 to burner i 23, fed withvv fuel through open valve |41 from fuel line |40 to burner |23. Chamber |0| is provided with chimney 4|, chimney valve |42, a number of spray nozzles |43 fed with oil through individual valves I8 from manifold pipe |55. Spray nozzles |44 admit water through open valve |30 from water line |29. The bottom of chamber |0| is provided with drain pipe |20 and drain valve |45.

The process of cracking the crude oil used in Illustrations I, II and III with the apparatus in Fig. 5 is as follows: Step I: On heat-The apparatus is cold. All valves except |30, |40, |42 and |41 are closed: 480,000 cu. ft. per min. of cold air from |32 enters louvers ||1, H1', passes upwardly through H5 and |2, downwardly through |00, upwardly through |05 and discharges through |42. Burner |23 is operated with 129,000 cu. ft./min. of air from |39 and 89.26 gals/min. of fuel oil from and open valve |41. Products of combustion from burnerv |23 mix with air from 5 (after passage through H6). 'Ihe amount of fuel is regulated to maintain temperature in conduits ||4 at 954 F. The

on-heat step is continued two hours ifty-ve minutes when chimney temperature at 42 is 937 F. thereby heating H4, H3, ||2, H0, |09, |08, |01, |00 and |05. Valves |38, |40 and |41 are then closed. Steam is admitted by opening valve 28, and the four chambers |0|, |02, |03,

and |04 are purged of air with steam. Valve |42 is then closed. Step III On stream-Pump 2 is started, nozzles are regulated to spray oil through spray line |43 from tank in a controlled manner onto the surface of bed |05. Oil at contact with the bed is heated, vaporized, superheated and partially cracked as it passes downwardly through |05.- Heated vapor enters |00 through |01, traverses |08, ||2, ||4 into open space 5 all at the mean temperature of .953 F. This vapor at 953 F. strikes the upper surface of ||6 and in downward passage therethrough is cooled, condensed, the condensate cooled and treated oil flows through ||0 and |33 to drain through |48 and opened valve |5| and cooler |49 into product tank |50. This on stream step is continued at the rate of 170 barrels per minute for twenty-one minutes twentyfour seconds, during which 3000 barrels of oil have been passed into 0|. During this onstream period, 465,000,000 B. t. u.s of heat initially in the upper 18 feet of bed |05 are transferred to 900,000 lbs. of oil, cooling this portion of |05 to 60 F. The temperature in |00 and ||2 is changed only by loss of heat through the walls and by whatever heat is absorbed or produced by the cracking reaction; both of which items are small. More than percent of the heat removed from |05 is added to the upper 17 ft. of ||6. All valves are then closed. Any liquid oil in |0| is drained through |20 and opened valve |45, |52 and cooler |53 into purge tank |54. Steam from opened valve |28 is then swept through the chambers discharging through opened valve |52 into tank |54. The apparatus is then blown back, i. e., is placed on heat. Air traversing ||6 discharges in l5 a few degrees below 953 F. A small quantity of fuel is burned at burner |23. As the blow back operation continues, the air from IIE discharges into ||5 with falling temperature and an increasing amount of fuel is fed to burner |23 to maintain ||3 at 954 F. Cold air from |32 cools |33 and the lower part of ||8 to 60 F. Hot air at 938 F. from |00 enters |00 through |01, heating v|00 and the lower part of |05 substantially to 930 F. Blow back continues at a flow of 620,000 cu. ft./min. of air from |32 for forty-two minutes, when chimney temperature at |42 is 925 F. The apparatus is then purged with steam and placed back on stream. The previous operation is continued.

Advantages attach to the operation described in Illustration IV; (l) A constant rate of flow of bbls./ min. results in a mean time of mean fluid transit through the four `chambers I0 l, |02, |03, |04 of 2.24, 1.56, 1.13 and 1.45 seconds, respectively. In traversing |05 at the start of the on stream period, an element of oil is heated rapidly and is subjected to 2.94% alteration during the 2.24 seconds the oil remains in chamber |0|. The volume of vapor at entrance into |08 is 224,000 cu. ft./min. measured at actual temperature and pressure. The volume discharged from ||2 at H3 is 480,000 Cu. ft./min., the increase in volume being caused by the change in mean molecular weight7 of the thermally treated hydrocarbon and to the formation of methane, hydrogen, and other non-condensable gases, due to the assumed unavoidable over-treatment. The time of transit of the mean duid element through |08 and l 2 is 2.69 seconds, during which time, at the temperature of 951 F., the cracking reaction is completed. At the instant of the completion of the reaction the treated vapor impinges on |6, its temperature instantly is lowered and the velocity of the reaction slowed down to an immeasurable rate in less than one-hundredth of a second. As on-stream continues, the amount of upstream cracking in |05 decreases as the upper portion of the pebble bed is chilled by incoming cold oil, the cracking in |00 and ||2 remains constant, and the downstream cracking in H6 increases as the upper portion of lili becomes heated to 956 F. by hot vapor entering through I4.

It is an advantage 44of this' particular embodiment of' the invention (Illustration IV) that the downstream cracking in Heincreases as the upstream cracking in decreases, yand that each increase 0r decrease is small and essentially compensatory, this requiring little change in the oil pumping rate during on stream. Operation in Illustration IV differs from Illustrations II and III chiefly in that cross-over 56 (Fig. 3) is functionally replaced by |01, |08, |09, H2, ||3 and |'|4 (Fig. 5). In Illustrations II and III, heating of oil, vaporization, vsuperheating vapor, and cracking all took place in a pebblebed, throughy which the thermal wave was moving. In Illustration IV most of the cracking takes place in an essentiallyisothermal cracking bed and the oil heating, vaporization and superheating, with its consequent thermal wave motion, are restricted to separate beds. While `this is frequently an operating advantage, it represents no fundamental difference. The fact that feed-stock is sprayed downwardly in one case and is pumped upward in the other is a casual result of engineering convenience, as is the rectangular -or cylindrical shape of the chambers 52a, 52h,

|'0|, 02, |03 and |04. In treatment of unstable fluids at elevated temperatures where there are vformed products which are unstablev at formachamber temperature is decreased 24 F., both temperature and rate are suitably altered, changes of little technical importance.

What would be serious, however, is the fact that were thesevchambers empty the heated oil would not move in stream line now; eddies, vortices, and turbulence would obtain, and the flow wouldl not be isochronous in transit. Dead corners would appear in the chambers, time would be excessive, and carbon and non-condensable gas formation would increase. With empty reaction chamber, the yield would be little if any better than in presentcracking process wherein open reaction chambers are used and fluid iiow is not under control. The chief object in providing beds |08 and ||2 is to direct the fluid flow in |02 and |03' and to prevent chaotic drifting about Vof fluid therein. The shape of |08 and I2 is determined bythe geometry of the walls of |02 and |03 and wall |3| and byshape and tilt of the'upper surface of' |08 and ||2 by the location of |'0"|` and ||0, and bythe shape and size of |09 and 'I'he several fluid elements in transit from |01 to ||3 should-follow trajectories of such length and at such velocities that the time consumed in transit by each duid element is the same. With proper design, it is the time of transit of the several fluid elements which is equal, neither the lengthof path'nor the velocity separately need be or necessarily should be the same. Velocity through the Ibed is determined by temperature, density, and viscosity of the fluid, by size. shape, and packing of the particles or pebbles and by the geometry ofthe interstitial voids. Advance calculation of such design is not always simple or accurate. In practice', of,v course, fluid flow can readily be made isochronous by analyzing Vfluid samples conveniently taken Vfrom selected points on the upper free surface of |08 and |l2. Itis usually found. however careful had been the chamber design, the screening of particles, and their bedding down, that fluid traversing one path is either (a) over-treated due to too long a transit time, a defect which may be corrected by substituting larger particles along that path, or (b) under-treated, due to too short a transit time, correctable by substituting smaller pebbles along the path to present greater resistance to fluid ow. Because the present invention can be carried out efficiently with such wide variety of structural design, the operator seldom experiences diiculty in approximating isochronous ow.

It is to be understood that for air as the carrier gasl another gas such, for instance,` as carbon dioxide, steam, or the like, may be employed.

Illustration V When small scale operation is contemplated and when a minimum of apparatus is an objective, a convenient embodiment of the concepts of the present invention can be carried out with the apparatus shown in Fig. 6. After .an initial heating step the apparatus is placed on stream as follows: Feed-stock from tank 20| heated to 234 F. by steam coil 202 is sprayed by pump 203 through nozzles 204 onto and intobed 208 in chamber 206, provided with insulation 20T, and supported on bed 209. 201 is constructed to provide open annular space 2 I3 through which steam at 1800 F. from ports 2|4 and bustle pipe 2|5 is introduced. Bed 209 rests on bed 2|0 supported upon a grid of cast iron bars 2|| positioned in 206 to form open space 2|2. At the start of on stream, 208 is at a selected reaction temperature, say 900 F. Oil traversing 208 downwardly is heated and progressively cracked in 208 and 209. Bed 2|0 was at 234 F. at the start of the on stream period. The treated fluid is cooled, and its reaction quenched as the product flows from 2 I2 through liquid exhaust 2 6, opened valve 2|| and cooler 2|0 into tank 2|0. Non-condensable gases discharge through 22|, through open valve 222, and are stored in a gas holder (not shown). On-stream is continued until a selected upper portion of 208 is cooled and/0r a selected upper portion of 2 I 0 is heated.

During the on-stream of 206, regenerator 230 is on-gas. Air from blower 233 through opened valve 230 mixes in burner 231 with fuel from fuel lines 238 and opened valve 239; hot products of this combustion traverse pebble bed 229, discharging through open space 228, chimney 240 and opened chimney valve 24|. The on-stream of 206 and the on-gas step may conveniently extend concurrently and terminate simultaneously. 'An on-steam step is now started. All valves are closed except 226, 221, 232 and 233. A regulated flow of primary or cooling steam from supply line 225 under control of valve 226 traverses 2|0 upwardly, entering 2|2 at 234 F. and cooling 2|0 to that temperature. Secondary or heating steam flows under regulation of valve 227 through bed 229, which had been heated to 1900 F. during on gas period. The secondary steam after heating flows through hot steam line 23|, open valve 232, bustle pipe 2|5, ports 2 |4, into annular space 2|3. The primary and secondary steam co-mingle, passing upwardly through 209 and 208, and discharging through exhaust pipe 234 and open valve 233. The primary steam after traversing 2l0 arrives at 209 and 213, heated to 900 F., mixing with secondary steam heated to 1800 F., the mixed steam traversing 208 at 907 F. As on steam continues, the lower heated portion of 208 broadens upwardly. On steam is terminated when chimney temperature at 234 approaches 900 F. and/or when temperature at the top of 210 is cooled to 234 F. 206 is then placed on stream and 230 on gas and operation is continued by cycling these alternating steps.

Beds 208 and 209 are feet in diameter and feet deep, consisting each of 105,000 lbs. of 3A; inch particles of blast furnace slag. During the on stream step, by partially closing valve 2H, pressure inside 206 is maintained at 350 lbs/sq. in. gage, and 2 barrels per minute of oil is forced through spray nozzle 204. At 900 F. molecular alteration of the oil proceeds at the rate of 0.35% per second, and the average time of the oil in the reaction Zone is just three minutes.

The apparatus described above, which uses steam for a carrier gas, is particularly convenient when located in a refinery plant having an ample and inexpensive supply of steam.

Although a considerable variation in plant construction and in operation appears in the preceding illustrations, at least one feature is seen to be common to all, viz. the fluid to be treated is passed through heat-interchangers of a type exhibiting prompt thermal response or a high efficiency of heat interchange. In heatinterchangers now employed in industry, fluid temperatures Tf at any position in the heatinterchanger differ greatly from the temperature of the solids, Ts, at that position. This is due to the prior art custom of designing the fluid channels of large dimensions, and of using heatabsorbing refractory of large dimensions and hence thermally sluggish, being incapable of rapid change of temperature. Complete economic success in the conduct of the present invention is dependent on the heat-interchanging characteristics of the above-described pebble beds or of some comparably efficient type of heatinterchanger.

The velocity of the reaction causing the molecular alteration of the unstable fluids contemplated in the present invention varies greatly with Tf, not with Ts. Except in the middle of the temperature wave front, Ts and Tf are approximately equal in the pebble-type of heatinterchanger frequently differing in practice by less than a degree or two, a fact not true in any other type of heat-interchanger used in prior practice. Such values of (VTS-Tf) as have been found here are smaller than would be anticipated from experience with heat-interchangers of the usual type used variously as blast furnace stoves, or as open-hearth, glass-tank, coke-oven regenerators. The coefcient of reaction velocity in oil-cracking is so great that satisfactory temperature-time control is found to be unsatisfactory in all of the several attempts to carry out the present cracking process with heat-interchangers of the types proposed according to any of the procedures heretofore described. Conventional assemblages of standard regenerator tiles have fluid channels of large cross-section and exhibit low coeicients of heat transfer. As a result, large differences between Ts and Tf obtain throughout the regenerator and control of Tf is diicult. Near the fluid-solid interface, it is true, Tf approaches ',I's closely; but at points remote from the interface,

TS-Tf is objectionablyY great. Furthermore, fluid velocities near the center of the channels are greater than those near the interface even when considerable turbulence is maintained. Hence isochronous flow cannot be approached at all closely in this type of operation; peripheral portions of the fluid streams move more slowly through the heating chamber than the more central uid elements, remain heated longer, and are heated to higher temperatures. Over-treatment, both in time and in temperature inevitably occurs. Thus, the so-called vapor phase cracking processes using such unresponsive regenerative interchangers are recognized to deposit excessive carbon and to produce objectionably large volumes of non-condensible gases. These defects have been thought to be inherent in all vapor-phase cracking processes. Over-treatment has not been chemically proven to be a fundamental characteristic of 10W pressure thermal treatment; it is merely an observed fact of practice that over-treatment has been unavoidable, which is an obvious result of the difficulty in maintaining low-density fluid (liquid or vapor) at any selected temperature, and of the decreased heat-transfer with low-density fluids and the greater departure from isochronous iiow prevailing when fluids of low density are treated compared with fluids of greater density. The object of the present invention is to provide means for treating unstable fluids to produce unstable products at any desired pressure. Frequently the composition of the desired product depends on the reaction pressure. In the present invention, operating pressures may vary from high vacua to high pressure to accommodate a variety of feed-stocks and of products produced. Reaction chambers such as 52a and 52h in Fig. 3 are internally heated and transfer of heat through the walls is not desired. The internally insulated metallic shell remains `cold and exhibits greater mechanical strength than can be realized at elevated temperatures. Since the metal is cold, reaction between metal Walls and sulphur is less. Carbon deposition (reduced to a minimum' in the present process) does not tend to carburize and weaken the metal. The maximum pressure is therefore limited only by structural dilculties in. metal fabrication, and is not further limited by loss of metal strength due to heating, oxidation, carburization, and sulphide formation.

Although the five illustrative examp-les given above describe the cracking of petroleum, it must not be thought that the present process is concerned exclusively or even principally with that reaction. The industrial importance of producing motor fuel from petroleum compounds perhaps justifies the over-emphasis implied in the selected illustrations. Furthermore, because of the accumulated experience gained by the oil industry in carrying out the cracking reaction, it has not been necessary to discuss the chemistry of the process. On the other hand, because identication of the compounds present in the feed stock and in the altered product in these five examples is possible only in the sketchiest fashion, the pyrolysis of petroleum is not the best choice of an example for describing the basic features of the present process. In illustrations following, the carbonaceous fluid to be subjected to molecular alteration at eleveated temperature is the simplest hydrocarbon known methane. Since rather complete knowledge is had of the thermal properties of the low molecular weight compounds involved (involving less than 7-carbon atoms per molecule) a fairly accurate quantitative description of the chemical changes taking place in the heated pebble beds can be given, and the characteristics of the present invention can be taught in satisfactory detail.

The production ofl ethylene from methane is readily effected by passing natural gas (freed from COzOiz and H2O)` through apparatus constructed in the fashion shown in Figure 3, and operated generally as was described in Illustration II. For the present example, the pebble beds 54a and 54h are built 14 feetV in diameter with an axial height of 5 feet, each bed containing 3,800,000 sandstone pebbles, screened through one-inch and on one-half inch, weighing 82,- 000 lbs., exhibiting 36.8% voids, 42,600 Sq. ft. of heat-exchanging surface, and a mean hydraulic radius of 0.073 inch. The roofs of chambers 52a. and 52h are built as 'at as practical and the tops of beds 5ta and 5th are brought up close to the roof to reduce the volume of open spaces 55a and 55h to a minimum. In the present example the volume of 55a, 5517 and' the cross-over 56 is y34.5 cu. ft.

In the preliminary heating step the beds are at 60 F., and all valves closed except 85a, 85h, 19a, 10b and 61a. For 16 minutes 51,800 cu. ft. per min. of standard air is vforced by draft blower 05 through burners 18a and 18h, while 2276 cu. ft. per min. of natural gas is fed to these burners from fuel feed line 63. Combustion in spaces 55a and 55h produces products analyzing 4.45% CO2, 10.20% H2O', 9.97% O2 and 75.38% N2 at 1970" F., which pass downwardly through bed 54a, heating the upper portion of the pebbles to1966 F. A thermal wave is established in 54a and at the end of the 1li-minute heating period the center of this wave is 48.3 inches below the surface of the bed. If L represents the distance in inches in the beds measured vertically upwardly from the grate bars 53a and 53h, and T the temperature of the pebbles in degrees Fahrenheit, then after 16 minutes `of heating T=1966 from L'=16.5 to L=60, T=1040 at L -`11.7, and from L='0 to L=6 the pebble temperature T is 116i7 F., the dewpoint of the combustion products atn which liquid water condenses from the downowing gases. In the 10.5 inch Zone between L=6 and .T ,=16.5 the temperature gradient (d/ dL) is great, 204 F. per inch. During heating the thermal wave is blown down the bed at the rate of 3.03 inches per minute.

Afterheating 54a for 16 minutes, valve Bla is closed, valve Gib is opened and combustion products are blown downwardly through 54h for 110 minutes, heating the pebbles therein to 1966" F. from L=34-4 to L=60, to T==l040 at L":29.'7 and T2116 from L= to 1:25. All valves are then closed. A direct ow step is initiated by opening valves 50a and SIb. In the example, I represents a gas holder containing natural gas. assumed to be essentially pure methane, and 2 represents a 2-stage centrifugal gas blower driven by a 3600 H. P. motor. A flow of 70,000 cu. ft. per min. of gas (measured at 60 F. and atmosperic pressure) is blown upwardly through 54a from left-to-right through cross-over 56 downwardly through M) out through 6 lb, to an ethylene recovery system (not shown). The natural gas passing through the apparatus experiences a pressure drop of 8.5 lbs/sq. in. The gas passes through the thermal wave front (L--S to 1 .:16

bed 54a) in 0.031 seconds, through the upperA heated portion of 54a (L=16 to L=60') in .049 second, traversing`A empty spaces 55a, 56 andv 5517 in .0074 second, and through the upper heated portion of 5th in (L -34.4 to.L=60) in .025 second, and is cooled` from 1966 to 11.6 F. in passing through the downstream wave front in 5th (L=25' to L=34.4) in 0273 second. In passage through the apparatus theA natural gasA is held at the reactive temperature (above 1700 F.) for 0.0907 second, is heated from 116 F. to 1700 F. in .027 second and is quenched back to 116 F. in 55117 in .022 second. The maximum rate of heating in the upstream wave front (L=6 to L=16, 54a) is 155,000 F. per second; the maximum rate of cooling in the downstream is 204,000 F. per second. These rates of heating and cooling of course are much higher 'than are obtainable with industrial apparatus of any design other than that contemplated in the present invention. To a close approximation it can be said that 70,000 cu. ft. per minute of natural gas here is instantaneously heated to a uniform temperature of 1964o F., held in contact with pebbles not hotter than 1956 F., held at that temperature for .091 second and then instantaneously cooled to its initial temperature of 116 F. It is through the operation of this novel type of heating that the thermal alteration of unstable carbon compounds is effected in the present invention. Both the temperature of the reaction chamber and the time which each molecule or" reactive gas is maintained at that temperature are under precise and determinable control.

On passing through bed 50a the natural gas CI-Ii) is subjected to molecular rearrangement through the progress of four reactions involving collisions between methane molecules:

forming ethane, ethylene, acetylene, and carbon, respectively. In the present case, ldue to the simultaneous effect of these four reactions, the volume of gas exhausting from 54a. into 55a increases from 70,000 cu; Ift./min. to 79,500 cu. ft./min. (measured at 60 E), having the composition: I

Percent by volume C21-I4 10.6": C2H2 0.73 C21-I6 lr'0.001 CH4 65.18 H2 23.45

The gas stream is subject to further expansion to 83,750 cu. ft.`/m'in. in passage through reaction chamber 52b, emerging with the composition:

Per cent C21-I4 14.05 C2H2 1.02 CzH .001 CI-I4 53.12 Hz 31.81

r involves the conversion in the chamber 52a (A) 16,920 cu. ft./min. of methane into 8462 cu. t./1nin. of ethylene, involving the absorption of 760,000 B. t. u./min. (90 B. t. u./cu. it. of ethylene), (B) 1160 cu. t./min. of methane into acetylene absorbing 270,000 B. t. u./min. (467 B. t. u./ cu. ft. acetylene) and (C) the deposition of 5.6 lbs. per minute of carbon by the thermal destruction of 176 cu. ft/min. of methane, absorbing 18,000 B. t. u. per minute. In addition to heating 70,000 cu. t./mn. of natural gas from 60 F. entrant temperature to 1966 F., requiring a transfer of 5,420,000 B. t. u./rnin. from pebbles to gas, an additional 1,048,000 B. t. u./rnin. of heat is absorbed from the pebbles in the bed due to the endothermic heat in the three methane conversions listed above as A, B and C. The total lheat transferred from the upstream pebble bed 54a to the gas is 6,468,000 B. t. u./min. (11,000 boiler horsepower). The heat required to bring the natural gas up to the reaction temperature is extracted from the wave front, and causes the thermal wave in 54a to recede upwardly in the bed at the rate of 7.46 inches/ minute. The heat absorbed from the pebbles by the formation of ethylene and acetylene, and in the deposition of carbon, however, is taken from the heated portion of the pebbles (in bed 54a from L=16 to L=60), causing a drop in temperature of 61.6 F./minute. In the downstream pebble bed 54h, the conversion of methane produces, at the start of the direct ow step 3318 cu. t./min. of ethylene and 272 cu. ft./min. oi acetylene with a concurrent deposition of 1.59 lbs. of carbon. The heat absorption due to these three sources is 441,000 B. t. u./ min. The total production of unsaturates per minute in the two chambers is just under a half ton, viz. 880 lbs/min. of ethylene and 100 lbs. of acetylene.

Direct flow is continued, with a 300,000 cu. ft. gas throughput, i. e., until 300,000 cu. ft. of natural gas has passed through the apparatus in the total time of 6 minutes, the rate of gas being decreased from the initial 70,000 cu. t./min. at the start, to 30,000 cu. ft./min. at the end or" direct flow. Bed 54a is cooled to 60 F. (entrant gas temperature) from L= to L=38. The center of the thermal wave (T=1040 F.) is at L=43.7, and the upper heated zone is only 12 inches in axial extent (L=48 to L=60). In the downstream bed 56h, however, the thermal wave has been shifted downwardly, the upper heated portion extending from L=60 downwardly to L=28.

During the direct flow step, the temperature of the heated (upper) portions of the two beds 54a and 54h decreases, as a result of the endothermic conversion of methane into ethylene, acetylene and carbon, and at the same time the velocities of these reactions are slowed down remarkably. The rate of ow of natural gas through the apparatus is diminished continuously throughout the G-minute direct ow period, to compensate for the decreased reaction rates. The total result of the direct flow step is: 300,000 cu. ft. of natural gas enters bed 54a. and 354,000 cu. ft. of altered gas discharges from 6th, this gas exhibiting an analysis (averaged for the G-minute period) of Per cent 02H4 13.63 C21-I6 0.001 C2H2 0.95 CH4 54.66 H2 30.76

In the recovery system (not shown in Fig. 3) there are extracted 3600 lbs. of ethylene and 232 lbs. of acetylene, and the gas leaving the recovery system, rid of its unsaturates, amounts to 302,300 cu. ft. of spent gas analyzing: 63.88% Cl-n and 36.12% H2. The average temperature of the heated upper portion of bed 54h is 1723o F. at the end of the direct flow step. During this step 109 lbs. of carbon soot has been formed a portion of which is trapped on the pebbles amounting to a fairly uniform layer of carbon from .0002 to .0003 inch thick. A part of the carbon black formed is swept out with the gas through Sib.

The gas in the apparatus is then purged with steam, by opening valve 96a attached to a source of steam not shown, and a reheat step is initiated. All valves are closed except 61a, 85h and 96. Blower 65D discharges 51,800 cu. it. per minute of air (at 60 F.) through open valve 39 into space Bib, which, passing upwardly through 54h, is (a) heated to the average temperature of 17 18 F. and (b) cools the lower part of 55h to 60 F., at the rate of 2.90 inch per minute. Natural gas is admitted from feed line 68 through open valve 655 to burner 780, and burns in spaces 55h, 56, and 55a at the flow rate of 316 cu. it./min. of gas having a low heating value of 970 B. t. u. per standard cubic foot. This reheat step continues 23.5 minutes, the total fuel gas being 7432 cu. it., corresponding to a net thermal input of 7,250,000 B. t. u. Of this, only 90.2% goes to restore the 6,540,000 B. t. u. loss in the endotherrnic production of ethylene, acetylene and carbon black. Heat loss through the brick walls (Q-in-ch rebricl; plus 9-inch of insulating brick) amounts to 2.12%. In the direct flow step 2.42% of the heat supply was discharged through chimney valve Sib, and 5.26% of the heat was discharged from 6la in the reheat step. Including time required for purging with steam at the time of valve reversals, the total cycle, direct flow, and reheat step consume 30 minutes. The daily consumption of gas in this operation is 14,400,000 cu. ft. treated, and 358,000 fuel gas, a total of 14,760,000 for 48 cycles per day. The products of molecular alteration of the natural gas totals 86.4 net tons (2,000 lbs.) of ethylene as primary product; with associated luy-products of 5.5 tons acetylene, 2.4 tons carbon black, and 14,500,000 cu. ft. per day of discharge gas from the recovery system analyzing 63.88% CII4 and 36.12% H2.

Illustration VII With apparatus identical with that used in Illustration VI, it is possible to convert substantial amounts of methane into acetylene. The gas to be heated can be natural gas, or, without serious loss of emciency, the 63.88% CI-I4 gas (spent gas) discharged from the ethylene recovery system of Illustration VI. The preliminary heating step described in the preceding example is carried out with the exception that the fuel gas is increased from 2276 cu. ft./min. (Illustration VI) to 2830 cu. ft. in the present case, with the result that the upper 44 inches of 56a and the upper 25 inches of 54h are heated to 2380 F. in place of the preceding 1966 F. The direct flow step is repeated as described, with the exception that a higher flow rate of gas is employed, i. e., 154,000 cu. ft./min. with a corresponding decrease in the time of contact between the passing gas and the heated pebbles. With increased flow the pebble bed may desirably be of larger diameter, e. g.,

screened through 2-inch and don 1.5 inch to prevent excessive pressure drop in the passing gas stream; with the greatly increased endothermic heat absorbed in the conversion of methane to acetylene (as compared with ethylene) the rate of decrease of pebble bed temperature is greatly enhanced, causing a very large change in reaction temperature during the progress of the direct flow step. The direct ow step continues for 90 seconds, in which time 152,000 cu. it. of spent gas from the ethylene recovery system is forced through the apparatus. The pebble bed temperature falls from 2372i F. to 2007" F. during this 90-second` period. The volume of exhaust gas is 196,570 cu. ft. and its average analysis is Per cent by Volume C2H2 9.63 CII-I4 26.90 H2 g 63.41

ing place 1n the direct flow step:

Gas passed through apparatus 38,000 76,000 114,000 152,000

Elapsed time in seconds 1.5 33 50 90 Gas composition: i

' per cent 10.97 10.46 9. 95 6.05 do 17 85v 23. 90 27. 30 40. 30 d 71.18 65.75 62. 75 53.05

f pebes F 231]. 22.y 07 2100 2037 Carbon deposited per cent.- 10. 2 55.85 27. 00 12. 00 Average rate vof iiow cu. ftJmin.. 154,000 126,00()` 93,000 71,000

At the beginning, the rate of destruction of methane according to Equation 4 is high, being 36.9% in. 0.01 second at 2372" F., falling to only 0.35% in 0.01 second at 20I2 F. The efliciency of methane conversion to acetylene depends upon adjusting the rate of flow of'gas to control the time the gas is at the particular temperature obtaining in the pebble bed, to permit the thermodynamically possible transformation of Equation 3 but to prevent excessive progress of the reaction given in Equation 4.

At the end of the S30-second direct 'ow step, a reheat step is carried out as described in Illustration VI. Because of the large pebbles in the present bed, the volume'o air from blower 65 can be increased to 95,000 cu. ft./min. without overloading the motor driving blower 65. Fuel gas from fuel main 68 is increased to 812 cu. ft./min. of natural gas and the reheat step continues 18 minutes and 30 seconds. With a ISO-second steam purging operation before and after the direct iiow step, a complete cycle (direct flow-steam purgereheat-steam purge) consumes 18 minutes, permitting 80 cycles perl day. The gas during direct flow discharging through '6 Ib is fed to an acetylene "extraction plant (not shown) in. which 1300 lbs. of C2H2 isy recovered from each cycle, totalling 52 discharge of 153600,000 cu. ft. from BTU, the" acetylene recovery system discharges 14,100,000 cu. it. of spent gas,` analyzing CH.; 29.79 and H2 '7 0.21. The total vgas used iny Illustration VII is 12,100,000 cu. ft. per day (treated in 54a and 54h) plus 1,250,000 cu. ft. per day of fuel gas (in the reheat step). A,

Iz'llustraton VIII The conversion of lmethane into hydrogenl according to Equation 4 of coul-'sel isVv easily realized by the present invention. The direct conversion of natural gas to hydrogen gives a maximum yield. 'I'he spent gas Jfrom Illustration VII, however, can readily enough be converted into H2 with the concurrent .production of carbon black. If itis desired tol'produce hydrogen `as nearly free as possible from methane, the fuel gas feed in the preliminary heating is increased to heat the pebbles to the highest practical tem.- perature. With usual firebrick and sandstone, or silica pebbles, 2600a Ff is a suitable temperature. At this temperaturel the speed of methane decomposition isV high enough '(40,000'% per second) so that equilibrium'is reached without need of slowing down the rate-fof blowing in order to realize minimum methane in the exhaust hydrogen. At 2600* F; the equilibriumpercentage of CI-I4 in the altered gas is 0.133%, with 9918671770 H2. By pushing the temperature up to a high value (using dead burned magnesite pebbles and basic refractory brick for lining), it is possible to lower this residualv mehane somewhat. For example, with the pebbles heated to 3100 F., the residual thermodynamically minimum methane is .055%. Above this temperature, reaction takes place between the carbon deposited on the magnesite (or dolomite) pebble and on the basicv refractory, producing magnesium vapor and `carbon monoxide. Because ofthe very rapid quenching in the wave front in bed 54h on direct ow, reoxidation of the' magnesium metal by' CO is inhibited, andthe hydrogen gas becomes contaminated with CO, a more seriousl impurity in 'the hydrogen than the methane.

In many industrial gases the carbon black produced is of greater importance than the hydrogen. Superior quality ofvcarbonv black can be produced at lower temperatures; and particularly by the rapid heating in the upstream Wave front (bed 54a). At the lower temperatures thev rate of blowing must be' decreased inA conformity with the sluggish rate of the reaction given in Equation 4. 'I'he carbon blackor powder, or soot, produced is largely blown outy of Sib with the emergent hydrogen, but some remains lodged on the pebbles. This coating of carbon is burned out during the reheating step, thereby diminishing the amount of fuel gas required in this step.

As an alternative procedure, the pair of stoves 12a and 12b (Fig. 3) 'can be operated as was described in Illustration III and used to preheat hydrogen gas, supplied in Illustration VIII, through conduit 92 (marked stean`1" in the drawing) through which steam was fed to 12a and 12b in alternate steps in Illustrationm. In the present example hydrogen producedin the process is fed back through 92 to pass upwardly through the heated pebble beds Ila. and 1lb to supply heated hydrogen through hot gas line and nozzles 96 into the cross-over 56, thereby supplying to the pair of reaction chambers 52a and 52D the heat absorbed in the endothermic reduction of methane. In this operative procedure, the re-heat step is omitted and the reaction chambers 52a and 5217 are operated alternately on direct flow and reverse ow as described in Illustration II. In this manner, no gas passes through 52a and 52h except CI-I4 and H2. The carbon dust deposited on the pebbles accumulates, and when the interstices between the pebbles become restricted, the beds of pebbles are removed from the reaction chambers 52a and 52o and replaced with other pebbles, and the carbon recovered from the mass of pebbles after removal.

In Illustrations VI, VII and VIII, three reactions are explained, all three of which, as it happens, being more or less endothermic, causing a decrease in the temperature of the pebble bed during direct and reverse flows, and requiring a reheating step in the operation of the auxiliary stoves 12a, and 12b to supply the compensating heat by the introduction of a highly heated gas (steam in Illustration II, hydrogen in Illustration VIII). The application of the present process is not conned to endothermic reactions. When the desired molecular alteration of the fluid to be treated generates heat instead of absorbing it, no reheating step is required, nor is it necessary to supply auxiliary heat from the pair of stoves 12a and 12b. The reaction between acetylene (produced in Illustration VII) and ethylene (produced in Illustration VI) is an important example of a strongly exothermic reaction.

Illustration IX Because of the low velocity of the reaction C2II4+C`2H2C4He (5) the apparatus shown in Fig. 5 and described in Illustration IV is convenient for use in the present example. Pebble beds |05, |08, l?.` and ||6 are heated as was described (Illustration IV) to the temperature of 1652", in the preliminary heating step. After purging the apparatus with steam,

and purging the steam with hydrogen, gas blower 2 (which was an oil pump in Illustration IV) forces 10,000 cu. ft./rnin. (measured at 60 F.) of a gaseous mixture of 57% ethylene and 43% acetylene (by volume) into the open space above pebble bed |05 in chamber |0|. The gas mixture flows through beds |05, |08, ||2, and H5 in series and discharges through exhaust pipe |08- and open valve |5| into the diolene recovery system |49 and |50. The time required for any portion of the gas stream to traverse the four beds is 3 minutes and 9 seconds. The volume of the gas mixture discharging into |49 is 8600 cu. ft./min. and its composition by Volume averages CALI-16:24.40

Two reactions takeplace in the pebble beds, (A) 2100 cu. ft./min. of acetylene combines with an equal volume of ethylene to form 2100 cu. ft./min. of 1.3 butadiene (all volumes measured at 60 F.) causing the generation of 367,000

Ill

24 B. t. u./min. of exothermic heat, and (T) 700 cu'. ft./min. of ethylene is converted into an equal volume of acetylene plus an equal volume of hydrogen according to equation Equation 6 being of course merely Equation 3 minus Equation 2, and thus does not represent any additional chemistry. This conversion of ethylene to acetylene is endothermic, absorbing 147,500 B. t. u.,/min. The walls or the four chambers in Fig. 5 are constructed with 9-inch firebrick enclosed in 27 inches of insulating brick, which maintains the heat loss through the walls to as little as 55,000 B. t. u./min. The net generation of heat in the beds is therefore 164,500 B. t. u. per minute, causing the pebble temperature to rise at the rate of 0.0515 F. per minute The direct flow step is continued for 12 hours, during which time the temperature of the pebble beds rises 37.2 F. The average bed temperature at the termination of the direct flow step is 1689 F. During this step the upstream wave iront is blown downwardly in bed |05 13 feet 6 inches, the rate of travel of the wave being constant throughout at 0.225 inch per minute.

The following step is not properly termed a reheating step but perhaps properly enough a blow-back step. After purging the chambers of the gas with steam, blower |32 is started, valves |88 and E42 opened, H8 and 45| closed, and 604,- 000 cu. ft. of air is blown through the four beds in series order, HE, H2, |08 and |05, for thirty minutes, thereby blowing the thermal wave in bed H6 upwardly and the thermal wave in bed |05 upwardly 13 ft. 6 inches, returning these wave fronts to the positions they occupied at the beginning of the direct ow step. In order to dispose of the exothermic heat generated by the reaction (Equation 5) between C2H2 and 02H4, 13,000 cu. ft. of the air from blower |32 is bypassed through conduit |39 and open valve E40, which auxiliary chilling air enters conduit i i4 at 60 l. commingling with the remaining 590,000 cuit/min. of air, leaving open space l l5 at 1688 F., thereby lowering the temperature of the gas entering l2 to 1652D F. The apparatus is purged of air with steam through |28 or by spraying water on the top of E44 through open valve in conduit |20. The apparatus is then purged of steam with hydrogen and a direct ow step immediately reinitiated. The cycle of direct ilow, steam-purge, blow-back. steam-purge,

hydrogen purge, consumes 12 hours and 35 minutes.

The total gas per day entering the butadiene recovery system agverages 11,740,000 cu. ft., containing 2,860,000 cu. ft. or" 143 butadiene (measured at F.) equal to 412,000 lbs. or 206 daily tons (2000lb.). The daily feed is 13,690,- 000 cu. ft. of mixed iuid to be altered, containing in the above described direct ilow step 7,800,-

5 000 cu. ft. of ethylene and 5,890,000 cu. ft. of

acetylene. The spent gas discharged daily from the butadiene recovery system averages 8,880,000 cu. ft. of acetylene-ethylenehydrogen mixture of analysis: C2H2 44.65, 02H4 44.60, and H2 10.75%. The gas returned from |49 and |50, stripped of its diolene content, can be recycled by adding, as make-up, 2,870,000 cu. ft. of ethylene (143 tons) and 1,930,000 of acetylene (65.6 tons). This process of re-cycling gas from the system |49 and |50, results in the continuous build up of H2 in the reactant gas, and results in a loss of tonnage, since the percentage conversion of olefines and acetylene to diolene is decreased due to the decrease in partial pressure of C2H2, C21-I4 and C4IIe in Equation 5.

Because of the low gas ow through the pebble beds in this example, the pebbles used may preferably be screened through 3/8 inch and on 1A; inch. The total weight of pebbles in the four chambers (Fig. 5) is 5670 net tons. The heat exchanging surface of pebbles exposed to the gas is 13,160,000 sq. ft. (300 acres). The time of passage of the gas through the heated zone is just over three minutes. Such a long heating time for the gas is necessary because of the low velocity of the butadiene formation reaction, when uncatalyzed. If the pebbles consist of quartz or pure silica sandstone, e. g., iirestone from northern Ohio, substantially free from iron oxide, the amount of surface catalysis is relatively low. But with the enormous area exposed to the gas and with the small mean hydraulic radius of the gas channels (0.03 inch) even soicalled catalytically inert silica, or clay, may readily double and triple the uncatalyzed reaction velocity upon which the above example is based. In illustrations I to VIII, supra, the uncatalyzed reaction velocities were very high, and some difliculty is experienced in shortening the time-at-temperature, i. e., the time at which the reactive fluid is held at reactive temperature (.T. A. T.), sufficiently to prevent excessive decomposition of reactants and products. In Illustration IX, however, the normal reactive velocity is so slow that very large scale apparatus is required for the small tonnage of product (200 tons/day). In the present example speeding the normal reaction rate is desirable. No particularly excellent catalyst is desired, nor is it difficult to discover. Silica, clay, glass and copper are not catalytically active. Finely divided iron, nickel and cobalt do speed up the reaction from 20 to 30fold. In the case of porous sandstone (running from 80 to 95 lbs. per cubic foot) pebble beds, in which the sandstone contains substantial amounts of FezOa, the FezOa is reduced to the metallic state by means of the H2 and (II-I4 of the` passing gas stream and by the carbon-black deposited in the pores of the sandstone lumps. When the large tonnages of heat exchanging pebbles are used, it is not, in every case, a desirable investment to save money on size of apparatus by spending money on artificially catalytic material. In Illustration IX, considerable improvement in recovery of diolenes can be effected by soaking the pebbles in solutions of iron, chromium, nickel and/or cobalt salts before placing them in the apparatus. The pebbles are heated to decompose the salts by oxidation to oxides, then passing H2 and/or CH3 gas through the apparatus to remove the oxygen. Operation at lower temperature is then possible with a substantial increase in the amount of 02H4 and C2H2 converted into 04H6. For example, at the pebble bed temperatures given below the equilibrium composition of a 50-50 mixof C21-I4 and C21-I2 is given:

Increasing the conversion of C2H2 and 02H4 to C21-Is decreases, of course, the diiiiculty of extracting the butadiene from the gas mixture entering the recovery system |49 and |50. The rate of conversion of ethylene to acetylene (Equation 6), however, is generally increased at the same time as the reaction of Equation 5 is` catalyzed, and it is the reaction equation which produced H2 that accumulates in the recycled reactant gas, causing operating dfculties, loss of materials and conversion costs.

Illustration X Temperature of Pebble Bed, F. 1800 1900 2000 `2100i 2150,

Perceutof 00H8 91.0 83.5. 67.2 37.0l 22.0 Percent of C2H2 9.0 16.5 32.8 63;() 78:0

Both the reactant C2H2 and the product 05H5 are completely unstable, the rate of their decomposition being high at all temperatures listed above. A convenient reaction temperature 'for the purpose of illustration is 2000 F. Apparatus constructed as shown in Fig. 3 will serve, with the pebble bed diameter 10 feet; bed depth r3 feet; pebbles screened through 11/2 inch on 11- inch; weight of pebbles 21,000 lbs, each bed; heat exchanging surface 7500 sq. ft. In the preliminary heating step carried out as previously de;- scribed, the upper 18 inches of beds 5taA and 5kb (Fig. 3) are heated to 2000 F., and a direct flow step is initiated, blower 2 forcing 3000 cu. ft./min. of acetylene through the two beds as described in Illustration VI. The volume of theA voids in the hot portion of the pair of beds is 87 cubicfteet, and the T. A. T. for the gas is 0.47 second. At 2,000o the rate of decomposition of C2H2 into carbon and hydrogen is 5.8 per second, causing the production of 2.54 lbs. of carbon black permin'- ute and 81 cu. ft. of hydrogen per minute. The volume of gas emerging from exhaustv B'lb and delivered to the benzene scrubber is 16.35 cu. ft. per minute with the composition (by volume):

Per cent CeHe 41.58 C2H2 24137 The high hydrogen content of the exit gas is due to the excessive production of carbon and hydrogen from the thermal destruction of the CSI-I6 during its formation, amounting to 33lbs. per minute in addition to the 2.5 lbs. of carbon formed from the acetylene during itsconversion to benzene. The production of benzene at: the rate of 681 standard cu. ft. per minute generates 507,500 B. t. u. per minute inthe pebble bed. The

decomposition of acetylene into hydrogen and carbon is endothermic, absorbing 22,000 B. t. u. per minute. The net heat generated is 485,500 B. t. u. per minute, causing a rise in bed temperature of 81 F. per minute. Direct ow continues for 3 minutes and 30 seconds, the apparatus is purged with steam, and a blow back step initiated in which 15,700 cu. ft./min. of air from blower in 65h is forced through open valve 99 into Sib upwardly through 54h, the air being heated to 2283 F., the final temperature of the beds 54a and 54h, after being heated 81 F. per minute for 3%; minutes. Auxiliary cooling air from blower 65 is forced through open valve 18h into space 55h, mixing there with the main stream of heated air emerging from bed 5422. The amount of auxiliary air from blower 65 is adjusted to maintain the temperature of the bed 54a at 2000 F. Because of the oxidation of the carbon trapped on the pebbles there is a tendency to an undesired rise in temperature in 54a. above 2000 F. This can be controlled by admitting steam through open steam valve 94a. The endothermic reaction between H2O and carbon is used to control the temperature in bed 54a. The blow-back step translates the thermal wave in 54h upwardly at the rate of 2 inches per minute. During the direct flow step the wave is forced downwardly at the rate of 1.24 inches per minute. When the blow-back step has continued for 2 minutes and 12 seconds, blowers 65 and 65D are stopped, the apparatus purged with steam, the steam purged with Hz and the direct flow re-initiated.

'I'he time of the complete cycle is 6 minutes and 30 seconds, permitting 220 cycles per 24-hour day. The volume of the exit gas through Sib entering the benzene scrubber (not shown) is 5722 cu. ft. per cycle or 1,256,000 cu. ft. per day. The benzene content of the exit gas is 54.3 net tons, i. e., 14,560 gallons per day, the benzene yield normally obtained from a battery of 230 by-product ovens coking 4800 tons of coal per day.

The daily discharge of benzene-free spent gas from the scrubber is 735,000 cu. ft. per day with the composition 41.70% C2H2 and 58.30% H2, which may be separated, returning the acetylene for recycling and providing 424,500 cu. ft of hydrogen as by-product.

The ten examples of practice described above illustrate the principles of the present invention as applied to the thermal alteration of petroleum to produce motor fuel and other petroleum products (Illustrations I to V), and to the heat treatment of methane and/or natural gas (Illustrations V to X) and to the products of such treatment.

The present invention comprises a thermal cycle exhibiting a close approach to thermodynamic reversibility and is not directed towards nor confined to any particular reaction. The method of operating the process as applied to the particular chemical reactions chosen for illustration has been described in considerable detail in which quantitative values for temperatures, rates of flow, gas composition, dimensions of the apparatus, etc., have been given. In any particular case the choice of operating variables, principally reaction temperature and time-attemperature (T. A. T.), is governed by the changes of enthalpy (AH) and entropy (AS) of the reaction on the one hand and the rates of the reaction itself on the other hand. At the temperature at which the desired reaction proceeds with satisfactory velocity, all of the carbon uids considered above are thermodynamically unstable, i. e., in the binary system, carbonhydrogen, the only stable state is the two-phase products solid carbon and hydrogen gas. Be- 5 cause of the large area of heat exchanging solid surface with which the gas is in contact in this process a complete absence of catalytic effect is difficult to obtain in practice. It is therefore impossible to specify with sufficient accuracy the proper T. A. T. for each reaction temperature. The figures used in the preceding examples are based upon so-called "uncatalyzed reactions, which are somewhat diicult to attain even in carefully constructed laboratory apparatus. The operator of the present process must be familiar with both the thermodynamic equilibria involved, but must make the proper engineering compromise between such equilibria and with the actual reaction rates obtaining in a given pebble bed. In the case of the cracking of petroleum, the proper time-at-temperature has been learned from past experience, to a large degree. With regard to many of the other reactions, even the thermodynamic properties of the system have not been widely known. In each of the equations given above the equilibrium composition can be determined from the free energy equation when k is the equilibrium constant, R the gas constant, and T the temperature in degrees Kelvin. In the case of the six reactions discussed in Illustrations VI to X, at the temperature at AH in calories per m01. and AS in calories/ C. per mol,

Because the entropy charge in Equation 1 is negative while AII is positive, no substantial amount of ethane can be produced by thermal alteration of methane. The production of ethylene and acetylene, however, is readily realized, AH and AS both being positive. The percentage conversion increases with temperature, but so also does the rate of decomposition of all three compounds CH4, C21-I4 and C2H2. Satisfactory results are attained by permitting an extremely brief time-at-temperature. Reaction 4 proceeds with no difficulty at all at elevated temperature, no maximum limit being imposed on the T. A. T., although the persistence of a stable tenth of a per cent of methane at maximum temperature proves an impurity if high purity hydrogen is required. Reactions 5 and 6 with AH and AS both negative attain best conversions at low temperatures. The velocities of both reactions are objectionably slow and percentage conversion must be surrendered in order to keep the time-attemperature at a reasonable figure.

'I'he more difficult factor in the operation of the present process is the determination of the reaction rate. For high molecular weight paraiiins an expression can be given as follows:

10g10v=42,5 1og1o(T/1000) +5.177-8.360/N where v=velocity in per cent per second, T is arman temperature degrees Kelvin, and N is the number of carbon atoms in the paraffin. Rates calculated from this equation agree with an average errorof about C. For the higher temperatures and for the lower molecular weight compounds, no general expression can be found. Annoying variations in observed reaction rates are partly clue to the difliculty of avoiding surface catalysis. In actual operation, however, an analysis of the gases leaving the reaction chambers will in every case indicate to the operator Whether his time-attemperature is too long.

Quite a number of important compounds, formed from the several hydrocarbons produced by the preceding examples, can be manufactured by subjecting CH4, C2H2, C21-I4, CeHe, Cil-Ie, etC., in the presence of each other and/or with H2O, HC1, C12, etc., to thermal treatment by the methods of the present process as described above. Among such compounds may be noted, phenol, toluol, styrene, isoprene, chloroprene and 2- phenyl-l-B-butadiene, according to the following reactions:

For a more detailed description of the thermal changes taking place in the pebble beds employed in the present process reference is made to my U. S. Patents Nos. 1,940,371 and Reissue 19,757.

I claim:

1. The process of decreasing the average molecular weight of a iluid reactant containing at least one carbonaceous component thermodynamically unstable and rapidly reactive at an elevated reaction temperature to produce a product of reaction by heating the reactant to the said temperature for a minimum length of time, suiiicien'tly long to eiect the said reaction to a predetermined extent, and for a maximum length of time, so short that an undesired amount of decomposition of reacted product is inhibited, which comprises, as a thermal adjusting step, establishing in -thermally insulated, broadly-extended, freely-bedded masses of relatively small, thermally responsive, refractory, solid, mineral particles a spatial distribution of temperatures comprising five zones of temperature in immediate mutual juxtaposition consisting in a cold zone, a thermal wave, a central hot zone, a second thermal wave and a second cold zone, the said rst and second cold Zones being substantially isothermal at such low temperatures that molecular alteration of the reactants and products are slow, the hot Zone being substantially isothermal at the said elevated reaction temperature, the rst thermal wave exhibiting large positive thermal gradients measured in the direction of fluid flow, and the second thermal wave exhibiting large negative temperature gradients similarly measured; and, as a irst operating step, forcing the fluid reactant to enter the first cold zone, to traverse the first thermal Wave whereby the reactant is heated to reaction temperature, controlling the rate of uid flow, whereby the duration of exposure of the reactant in its passage through the hot zone is ldelimited ,between .the said maximumA and, minimum, whereby the reacted product is rapidly quenched to inertness in transit through the second thermal Wave, and whereby the reacted product is .discharged through the second cold zone; continuing the first operating step while as (1) the two thermal waves are convectively displaced in the .direction of uid flow, (2) the first cold zone increases in spatial extent, (3) the second cold zone decreases, and (4) the central hot zone is subjected to displacement through the particles; terminating the first operating step before the disappearance of the second cold zone: and, as a second operating step, forcing the fluid reactant to traverse the said ve zones in reverse sequence, whereby the translation of the two thermal waves and oi the hot zone is reversed in direction and While as the second cold rone increases and the rst cold zone decreases; continuing the process as a repetitive alternating succession of i'lrst and second operating steps, while as the hot zone is repeatedly reciprocated within the massed particles, the spatial extent of the two thermal waves continually and irreversibly increases, and the temperature gradients therein decrease in absolute magnitude; and terminating the described succession of first and second operating steps when the thermal waves cease sharply to dene the said ve zones.

2. The process described in claim 1, wherein, after the termination of the alternating succession of first and second operating steps, due to the thermodynamic degradation of the said thermal waves, the initial temperature distribution is restored by a repetition of said thermal adjusting step.

3. The process of heat treating a carbonaceous fluid reactant to form reaction products of al- 40 tered average molecular weight which comprises,

as a thermal adjusting step, establishing a spacegradient of temperature within thermally insulated, enchambered masses of chaotically deposited, relatively small, heat-resistant, solid, mineral particles, the said distribution being characterized by the mutual juxtaposition of a terminal cold zone, an intermediate transition zone, a centra] hot zone, a second intermediate transition zone and a second terminal cold zone, the temperature of the said cold Zones being suiiciently low to inhibit appreciable reaction, the temperature of the central hot Zone being sufficiently high to promote a rapid rate of reaction, the two said transition Zones exhibiting large thermal gradients; as a first operating step, causing the fluid reactant to traverse the said ve zones in the order` named whereby it is heated, reacted and quenched in the said transit; as a second operating step, causing the reactant to traverse the said iive zones in reverse order; continuing the process in an alternating cyclic succession of the said first and second operating steps, while as the central hot zone reciprocates in the massed particles and the two transition zones are thermodynamically degraded and increase in spatial extent; terminating the said cyclic succession of operating steps when as, due to the said expansion of the transition Zones, insufficient space remains for further reciprocation of the central zone; and thereafter re-establishing the initial thermal distribution by repeating the said thermal adjusting step.

PERCY H. ROYSI'ER.

(References on following page) REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Smith Apr. 3, 1923 Porter Oct. 7, 1930 Wulff July 11, 1933 Royster Dec. 19, 1933 m Number 32 Name Date Winkler Jan. 8, 1935 Pyzel Aug. 31, 1937 Rogers Sept. 26, 1939 Porter Jan. 2, 1940 Martin Jan. 9, 1940 Duncan July 16, 1940 Hall Oct. 8, 1940 Bradley Feb. 3, 1942 Hasche May 18, 1943

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