US3843744A

US3843744A - Controlling coke in the pyrolysis of hydrocarbons to acetylene and hydrogen

Info

Publication number: US3843744A
Application number: US00225719A
Authority: US
Inventors: L Kramer; J Happel
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-02-14
Filing date: 1972-02-14
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22
Also published as: JPS5238002B2; FR2172148A1; BE795403A; NL7301998A; BR7301095D0; IT979033B; FR2172148B1; DE2307300A1; JPS4891001A

Abstract

A method for controlling and diminishing the formation of coke on the walls of reactors wherein hydrocarbons are undergoing pyrolysis and especially pyrolysis for formation of acetylene, which comprises injection of steam and/or an inert gas at at least one critically located point in the system downstream from the feed injection. The improvement step prolongs the period of introduction of feed to the pyrolysis by reducing the frequency of feed interruption in order to remove coke build-up.

Description

United StatesPatent 1 1 Kramer et a1. 9

[ 1 Oct. 22, 1974 METERED METHANE/FEED 3365387 [/1968 Cahn ct a1. 208/48 3,487 12l 12/1969 Hallee 208/130 X 3,507 929 4/1970 Happcl ct a1. c. 208/48 X 3.551.512 12/1970 Keckler et a1. .f. 260/679 Primary Examiner-Delbert E. Gantz Assistant Exuminer-juanita M. Nelson Attorney, Agent, or Firm-E. Janet Berry; Lawrence Roscn [57] ABSTRACT A method for controlling and diminishing the forma- I tion of coke on the walls of reactors wherein hydrocarbons are undergoing pyrolysis and especially pyrolysis for formation of acetylene, which comprises injection of steam and/or an inert gas at at least one critically located point in the system downstream from the feed injection. The improvement step prolongs the period of introduction of feed to the pyrolysis by reducing the frequency of feed interruption in order to remove coke build-up.

13 Claims, 4 Drawing Figures I I l I I l ELECTRICALLY m WINDOW HEATED 1 l REACTOR l f 7 1 I g' l I 1' I QUENCHING l CHAMBER 4 SAMPLE AND PRODUCT RECYCLE BY-PAss LINE CYCLONE SEPARATOR COOLER WATER DRAIN 8 RE'CYCLE PUMP mama M122 mm 3.843.; mm SHEET 1 BF 4 fgfEYE m REACTOR WINDOW [FEED TEMPERATURE INCREASING WW cooRs A099 H REACTOR TUBE o 3 ID. 2

MAXIMUM REACTOR w TEMPERATURE- ILLUSTRATIVE MAx ZONE OBSERVED COKING ZONE QUENCH END aawgfmm METERED CARRIER LINE HEATER VAPORIZ ER SHEET 2 OF 4 )LINE METERED WATER(STEAM CONTROL VALVES HEATED REACTOR D E F E m H T E M D E R E T E M PRODUCT Qp coomz X SAMPLE AND RECYCLE BY-PASS LINE SEPARATOR RECYCLE PUMP \CYC LONE QUENCHING/ CHAMBER PATENTEDHBT Z IIII 3M3; WW SHEET 3 0F 4 IOI STEAM INJECTION TUBE 3/16" NOM. 0.0.

g |/4"NOM. I0. I03" REACTOR TUBE WATER COOLED H x fouTER WALL I '08 O ZIRCONIA RETAINING WALL Ci I06 REFRACTORY A D ALUMINUM SILICATE INSULATION GRAPHITE HEATER ELEMENT STEAM VENT K [04 ANNULUS CONTROLLING COKE IN THE PYROLYSIS OF I-IYDROCARBONS TO ACETYLENE AND HYDROGEN This invention relates to an improved method for controlling the formation of coke on the walls of reactors wherein hydrocarbon pyrolysis is conducted. In particular, this invention relates to an improvement in high temperature pyrolysis systems for hydrocarbons wherein the desired product is acetylene, and the other principal components of the product stream are mainly hydrogen and lesser amounts of methane and ethylene.

Coke formation on the walls of hydrocarbon pyrolysis equipment is undesirable in that the coke is cumulative and eventually restricts the flow of the feed gas to such a great extent that the pyrolysis process must be interrupted for removal of the coke. When this coke cannot otherwise be controlled, it is burned-off in cycles by substituting an oxidizing gas such as air, steam, carbon dioxide or oxygen for the hydrocarbon feed. It is obviously desirable and particularly in commercial operations to extend the pyrolysis cycle as much as possible, because the coke removal cycle is a non-productive period and damaging to the reactors.

It is an object of the invention to provide an improvement in hydrocarbon pyrolysis processes for production of acetylene and hydrogen.

It is a further object of the invention to injectsteam or an inert gas at a predetermined location in the reactor to retard coke formation or remove previously formed coke.

It is another object to carry out the pyrolysis of hydrocarbons to form acetylene and hydrogen in an improved manner to minimize or avoid formation of coke.

Other and further objects will become apparent from the detailed description presented hereinbelow.

In comparatively low temperature processes, for instance those below 1,200C., such as the pyrolysis of hydrocarbons to a desired product or products such as ethylene or otherhigher molecular weight olefins, it is a well-known practice to dilute the feed with steam, and in this way to retard continuously thecoke formation. An undesirable feature of this method of coke control is occurrence of the water-gas reaction between hydrocarbon and steam and which yields carbon monoxide as an undesirable byproduct. At these low temperatures, this water-gas reaction can be controlled so that carbon monoxide yields are minimized. However, as the operating temperature is increased either to increase the ethylene yield or to increase the ratio of acetylene to ethylene in the product gas, the yield of oxygenated carbon products CO and CO increases. For example as shown by Reid and Linden, Chemical Engineering Progress 56 47 1960), over the temperature range of 1,240C. to 1,475C. (maximum reactor profile temperature), the combined concentrations of CO and CO produced ranged from 12.5 to 239 percent of the combined concentrations of ethylene and acetylene produced. Generally, the increased production of CO and CO follows conditions of increased severity of pyrolysis i.e., increasing temperature and- /or increasing reaction time).

As the temperature is raised still higher to a practical level for the production of acetylene, i.e., 1,450C. to 2,000C. as described in U.S. Pat. Nos. 3,156,733;

3,156,734; and 3,227,771, the use of steam to control coke build-up becomes impractical, because substantial degradation of the feed to the undesirable byproducts, CO and CO occurs with a concomitant de crease in acetylene yields. To date, no method for inhibiting these water-gas" reactions at these temperature levels has been reported.

During an experimental study of heat transfer in the pyrolysis of hydrocarbons to acetylene, it became necessary to observe the interior of the reaction zone; in particular, itwas considered desirable to determine where, within the reaction zone, sufficient soot (carbon) was present to cloud the gas stream. To facilitate this determination, a window was installed to permit observation of the entire reactor interior which consisted of the inner volume of an empty 3/8 inch inside diameter (1.D.) by 8 inch long alumina tube as shown for example in FIG. 1. The remainder of the experimental system has already been described for instance in Us. Pat. No. 3,156,734.

During the pyrolysis of a feed containing 34.1 mole percent methane and the remainder hydrogen, an unusual and unexpected observation was made. When feed wasfirst admitted to the reactor, for a short time the entire reactor tube volume remained totally clear to the eye and it was possible to look right through the reactor and into the quench zone. After a short time, as a mist or fog formed, its formation was extremely 1ocalized and occurred between the point of maximum profile temperature and the quench, nearer to the quench but within the reactor. Wlhen coke formed, it formed in the same localized area. This coke was burned out. The experiment was repeated many times and using other feeds, always with the same sequence of results as those described above. Typicalof these experiments are the data tabulated in Table 1 below.

The feed used was 34.1 mole percent methane and the remainder hydrogen at 31.2 X 10" standard cubic feet per sec (0C, 760 mm Hgab). The maximum profile temperature was 1,700C. to 1,725C., at We inches from quench (reactor outlet). At the start of feed flow the reactor volume appears completely clear and the quench appears as a dark disc at the bottom of the bright reactor walls.

TABLE 1 Time, Minutes from Start Pressure Drop,

Reactor clear, quench is a dark disc Mist appears inside reactor just before reactor exit Faint coke ridge appears on wall just before reactor exit Ridge of coke grows from wall towards center axis of reactor tube. No other coke or mist is visible at upstream locations Ridge of coke has grown to a plane'or sheet across reactor, obscuring quench zone, having a pin hole for gas flow, a

second sheet of coke is growing from wall on top of first sheet Pin hole in sheet closed; new hole opened Solid sheet across reactor with either cracks or platelet edges showing zero 1 OLII Mechanical probing of the sheet indicated that it was very thin, less than one-eighth inch thick. No other coke was observable until this thin zone, located between the maximum reactor profile temperature and the quench, but much closer to the quench, was substantially blocked. Only then did coke appear upstream and it had the appearance of water droplets on a swcating pipe. Similar results were obtained. for example, with a feed containing 25.6 molc methane except that the rate of coke growth was slower.

As a result of these observations, it is clear that the pyrolysis cycle (as distinguished from the decoking or burn-out cycle) could be greatly extended if this localized coke formation in the downstream end of the reaction zone could be controlled or retarded.

While it is not intended in any way to limit the processes or advantages of the invention to a theory, it was found advantageous to advance some possible reasons for this surprising, localized coke formation particularly in order to better formulate an experimental program for its control; some but not all of the reasons proposed are included in the following detailed listing.

The localized coke forms where:

l. The conditions for the rapid polymerization and/or decomposition of acetylene are first encountered.

2. Free radicals, present and relatively stable at the higher temperatures of the reaction zone, first reach a temperature where they can recombine as coke precursors and/or initiate polymerization.

3. High molecular weight species, already formed, reach a dew point.

4. Electrical forces at the interface between the reactor and the quench zone cause agglomeration and deposition of coke precursors.

As a result of these surprising observations, it was decided to attempt to control this coke laydown by injecting a gaseous substance into the product stream at some point downstream of the maximum reactor profile temperature but upstream of the point at which the localized coke forms.

In some cases, it is difficult to establish the location of the maximum of the longitudinal temperature profile of the reactor (along the direction of flow); for example, when a relatively flat, long zone rather than a point, is found at the maximum temperature. Then, for the purpose of the hereinafter described invention, Tmax is that location (point) in the reactor which is approximately at the maximum temperature observed within the reactor and which is furthest downstream (closest to the quench). In other words, the gaseous stream would necessarily be injected downstream of the high temperature zone of the reactor.

With respect to the hereinbefore stated proposed reasons for this observed localized coke formation and the possibility of injection of a gaseous stream to control this coke, it became necessary to select an appropriate gas. Two readily available gaseous substances were immediately considered, i.e., steam and hydrogen.

Both steam and hydrogen are reactive gases at high temperatures and may be expected to react with radicals or highly unsaturated coke precursors. Both gases would act to dilute the products and in this way reduce the rates of polymerization and the dew point of coke precursors. Steam has the additional advantage that even at temperatures substantially below Tmax, it reacts with coke, and therefore could be expected to reduce the net rate of coke formation still further. Both steam and hydrogen were also considered to be interesting from a practical point of view in that both are This, in conjunction with the paragraphs that follow should distinguish between steam and/or H in our process and either or both as a quench-or diluent.

Steam has been used many times as a diluent for the feed to pyrolysis systems and also as a quenching medium injected downstream of the reactor, and in both cases it has been found ineffective in controlling coke. When mixed with the feed, it prevents coke laydown, but, as shown above, because of the water gas" reaction it converts much of the hydrocarbon to carbon oxides (monoxide and dioxide) rather than to acetylene and thus the yields of the desired product are poor. As a quenching medium it has no effect whatever on reactor coke formation.

However, in carrying out the process of the present invention, the injected gas, i.e., steam and/or hydrogen, is separate from the feed and injected, hot, into the product just before the zone of localized coke formation described above. Since by this technique the temperature and time for the water gas reaction are thus both minimal, the production of carbon oxides is greatly reduced.

In addition to controlling the formation of localized coke, a further benefit results when the injected gas is heated externally from the reactor and then introduced upstream of the point of localized coke formation; the heat load and the size of the reactor can be reduced, said reductions being impossible when steam and/or hydrogen are used as feed diluents.

When steam was used to carry out the improvement of the invention, it was necessary to add a relatively small amount of a non-condcnsihlc gas, such as hydrogen, to prevent hammering and condensation in the very small steam lines used to carry steam into the furnace. This is an additional improvement feature of the invention.

Although coke formation is a problem encountered in the pyrolysis of all hydrocarbons to acetylene, the experimental results reported herein were particularly directed toward use of the improvement with methane as feed, because the coke control process described herein applies to that portion of the reaction zone where a substantial part of the pyrolysis process has been completed. Under these circumstances, the hydrocarbons present in the product stream are remarkably the same regardless of the hydrocarbon fed, and it is on this part of the stream, i.e., in the reactor that this carbon control process is peculiarly applicable; the similarity of the product stream components is illustrated below in Table 2 in order of decreasing concentration:

TABLE 2 Reference Product Feed US Patent 3,l56,733

US Patent 3,l56,734

US Patent 3,l 56,734

US Patent 3,227,77l

US Patent 3.227.77l

Hydrogen. acetylene,

methane, ethylenes Hydrogen, acetylene,

methane, ethylene Hydrogen, nitrogen, methane, acetylene, ethylene Hydrogen, acetylene,

ethylene, methane Hydrogen, acetylene,

methane, ethylene Hydrogen, acetylene.

methane, ethylene Hydrogen, acetylene,

(pure methane) (methane-hydrogen) hydrogen-methane-nitrogen methane, ethylene It is clear from the foregoing that the localized coke control process described herein cannot distinguish between different hydrocarbon fced gases which may be used, and would function similarly in controlling the localized coke formation regardless of the hydrocarbon fed to produce the acetylene.

Besides the localized coke formation herein described, there may also be formed that type of coke which is laid down more or less uniformly and at a much lower rate over the reactor-zone walls; for this type of coke, the use of injected steam offers an additional benefit. This coke may be removed by diverting or adding steam to the reactor inlet with or without shutting down the hydrocarbon feed. Obviously however if steam is added with feed flowing, the rate of coke removal will be slower and the production of carbon oxides increased.

EXAMPLE 1 An illustrative arrangement for use in the practice of the invention is shown in the accompanying schematic flow diagrams FIGS. 2 to 4. FIG. 2 is a diagrammatic representation of the elements of an apparatus wherein the metered hydrocarbon feed in line 1 which may be suitably diluted with hydrogen if desired is passed through one or more meter valves and then caused to pass through an electrically heated reaction chamber 3 and is then rapidly quenched in quenching chamber 4.

. Additionally, a separate and distinct, metered steam flow which may be diluted with a non-condensible carrier gas, preferably hydrogen, is admitted to a ceramic tube 6 passing through the same electrically heated re action chamber. Thus, for example, the maximum temperature within the reactor will be maintained in a range suitable for acetylene production, e.g., l,750C. maximum profile temperature. Thehydrocarbon feed, suitably diluted with hydrogen which is either premixed therewith or fed separately, is withdrawn from storage, metered and passed through suitable control valves. The pressure of the feed is measured and this feed stream proceeds to the electrically heated reactor 3. Similarly, a metered stream of steam and carrier is admitted to the ceramictube 11 via

lines

2 and 5 which tube passes through the reactor.

A suitable reactor for carrying out the herein described'process is seen in inside elevational view in FIG. 3 and in cross section in FIG. 4. As represented in these drawings, which are intended to be illustrative only for use in practice of the invention and not in any way limitative thereof, the reactor isseen to be FIG. 4) a concentric system of cylindrical tubes (or layers) which are progressively larger in diameter. The smallest and innermost tube 101 is ceramic and carries the steam through the reactor to the vent point 102 where it is admixed with, the hydrocarbon product stream which flows in the annular space 104 between this innermost ceramic tube and the next size ceramic tube (i.e., the reactor tube) 103 concentric with it. The vent point is conveniently located just upstream of the point at which the sheet of coke forms. The ceramic steam and reactor tubes are 3/l6 inch outside diameter (OD) (101) and 5 4 inch inside diameter (I.D.) (103) respectively and the annulus 104 positioned between the larger diameter reactor tube and the smaller diameter steam tube thus constitutes the reactor cross section of 1/32 inch nominal width. The narrow annulus 104 was not chosen because its performance I i.e., operating time: Time in Table 3) is the best, but because is very sensitive to coke and thus offers readily and quickly available comparisons of coking rates under different experimental conditions. Since it is unlikely that any production design would have smaller clearances, the operating times presented in Table 3 may be considered in the minimal ranges of those which would be encountered in larger reactors.

The ceramic reactor tube (alumina) is positioned within the graphite resistance element 105 designed to use low voltage electrical power up to 3.5KVA, thus providing sufficient heat to effect the maximum temperature within the reactor and steam tubes so described hereinabove, e.g., l,750C. the optimum temperature for production of acetylene.

Successive cylindrical walls of refractory 106 and insulation 107 are refractory walls of zirconia 106 and aluminum silicate insulation 107 within a furnace outer wall 108 of aluminum are desirably employed. The outer walls of the reactor are preferably water cooled. A window 7 FIG. 2) is positioned in the outer cylindrical wall 108 of the reactor to permit observation by an optical pyrometer sighting on the outer wall of the ceramic reactor tube (through slits in the insulation, refractory and graphite resistance element); thus a means for determining the temperature thereof is conveniently provided.

Upon leaving the annular reaction zone 104 the combined effluent stream containing product and byproduct, steam and carrier enters the quenching chamher 4 where rapid cooling of the hot effluent gas to a ture reduction by dilution. Additional cooling in a water cooled heat exchanger 10 for example further reduces the temperature of the effluent to ambient temperatures thus causing further condensation of the steam. Condensate and soot are desirably separated from the effluent; for instance this can be accomplished in Cyclone separator 9. Analysis of the gaseous effluent components'is accomplished by gas chromotography.

It will be evident that a variety of suitable systems and reactors may be employed for the practice of this v to a sheet form but to distinguish that coke which forms over a relatively short length of the reactor walls, grows rapidly out from the walls and forms only between Tmax and the quench (or shock cooling) zone fromthat coke which lays down at much lower rates both upstream and downstream of Tmax and covering the entire reaction zone walls more or less uniformly. Although in the particular system described herein, the temperature of the steam at the point it is admixed with the product effluent is the same as the reaction zone temperature at this point, this is not necessarily a requirement for operation of the invention and to obtain its advantages it is required only that the injected gas, e.g., steam, be hot, i.e., over 750C. If steam temperature is higher than the reactor temperature, the production of carbon oxides is increased.

Furthermore, the gas, e.g., steam, for injection into the system as described herein, comes in parallel, but separate from the feed. Other means for introducing this steam are also suitable and may be used; illustrative of but not intended to be limitative thereof, are countercurrent injection through the reactor exit (quench zone), and also, through a break in the reactor wall such that the gas enters the reactor perpendicular to the direction of feed flow from outside the reactor. In large and/or non-circular reactor configurations, parallel flow is the least desirable technique.

For any given reactor configuration and system, the point of secondary gas injection is best determined by experimentally conducting a short pyrolysis cycle until the pressure drop across the reactor (inlet to quench) is about one-eighth of the pressure in the reactor. Ex-

' amination of the furnace, after shut down in an inert atmosphere (e.g., nitrogen) will show where the socalled sheet coke is forming. Secondary gas is then injected upstream of this point, desirably as close to the point of coke formation as practically possible for the reactor system.

If it is inconvenient or impossible to open the furnace for examination steam injection through a movable lance can be used to determine where coke control is achieved within acceptable levels of carbon oxides production; this will conveniently locate the point for gas injection.

EXAMPLES 2-4 The following additional examples taken from a large number of experimental determinations are intended to be further illustrative but not limitative of the decreased coking rate and prolonged prolysis cycle achieved by practicing the improvement of this invention.

Particularly while the hydrogen to carbon ratio of the feed gas described is about 7.6 (atom H/atomC), the advantages of this invention have been demonstrated over a much wider range, 6 to 10.

Also, for economic reasons, it is often desirable to minimize steam consumption (lbs. of steam/lbs. of hydrocarbon fed). The minimum amount of steam which can be used will depend upon the parameters of the reactor in which the pyrolysis is conducted parameters such as length, cross section area and shape, temperature profile, etc.; however, in the reactor design illustrated below, ratios of 0.5 and less are effective.

Table 3 shows the operating conditions and results obtained during three sets of experimental runs 2a, b, and c; 3a, b, and c; and 4a, b, and 0. At constant feed composition and relatively constant conditions of temperature, it is clear that the following conclusions can be drawn from the data of these runs with regard to sheet coke control and the formation of oxygenated carbon compounds (almost entirely C0; C0 production is negligible):

1. From all examples, the pyrolysis cycle with steam is substantially longer than the cycle with hydrogen and both are much longer than that with no gas injected other than the feed. Thus in Examples 2 to 4 cited herein, the pyrolysis cycle time with hydrogen injection alone is increased over a range of 60 to 150 percent and the improvement with steam increased over a range of 100 to 200 percent as compared to the reactor operation without the invention. All times taken are that time to reach a pressure drop of one-half psi.

If the pyrolysis cycle is further continued to the point where the pressure drop reaches or exceeds 2.0 psi, then, as seen in Example 3, an increase in the pyrolysis cycle time of over 100 percent is attainable with steam as compared to no injection i.e., invention not operating).

2. The yield of CO can easily be limited to less than 5 percent of feed disappearance where a substantial portion of feed disappearance over percent, in all examples, has been converted to acetylene.

3. The yield of CO will increase as the point of steam injection ismoved upstream, that is, in the direction away from the quench.

In Table 4, the product analyses is shown for the total product exclusive of condensed water and carbon, and

also for that portion of the product based upon the feed- (carrier excluded). In Table 4, the terms CO, C,,, C C Y, and Y are used and their meanings are defined as follows:

Co moles methane disappearing per I00 moles of methane fed per pass. I

Ca moles methane converted to C H per moles of methane fed per pass.

CE moles methane converted to C l-I per 100 moles of methane fed per pass.

Cco moles methane converted to CO per 100 moles of methane fed per pass.

YA moles methane converted to C l-l per 100 moles of methane disappearing.

Yco moles methane converted to CO per 100 moles of methane disappearance.

It is to be noted that the analyses presented do not include other hydrocarbons produced and/or CO some of which appeared in all runs but only to the extent of about 0.5 percent (mole) or less and generally. their total amount did not exceed about 1 percent; water vapor was not considered part of the analyses nor was nitrogen and air which did not come through the reactor. The CO component found to be present when no steam is used probably arises from water in the quench recycle steam, but is nevertheless included for completeness.

TABLE 3 CONDITIONS AND RESULTS OF RUNS Tmax Steam Time Gas Flow* at in from run SCF/sec X 10 inches Pressure inches start (C, 1 atm abs) from drop from Example mlnzsec Feed H O carrier C quench psi** quench Sample 221 4:30 17.4 29.0 9.10 1770 2 1h 1 10-3 17:00 17.4 29.0 9.10 1760 2 A 1 13-3 20:00 1760 2 Va 1 211 4:00 17.4 0.0 9.10 1760 Z /11 1 14-3 12:00 1760 2 /4 1 1 6:00 1760 Z 4; 1 2L 5:00 17.4 0.0 0.0 1760 2 V; 1 14-4 6:15 1760 2 4 1 311 3:00 11.10 30.0 9.10 1700 Z A 1 10-] 23130 12.75 29.0 9.05 1750 2 1 13-1 24:00 A l 45:00 12.75 29.0 9.10 1750 2 1 14-1 47:30 2% l 31) 4:30 12.85 0 9.15 1765 2 1 10-4 7:30 0 V; l 1 1:00 0 l 36 3:00 12.85 0 0 1765 2 V2 1 13-4 3 :00 0 0 1 1 4:10 0 0 5 1 4L! 6:00 14.39 29.5 8.65 1740 1% 1% 13-3 16:00 14 30 28.0 8.70 1760 1% 1% 14-3 30:00 V4 1 A 41 L45 0.0 74 l /1! 18:30 14.48 0.0 8.65 1760 1 /41 13-4 20:00 0.0 1% 1%: 41' 10:00 0 0 l4 1 A 12'00 14.48 0 (l 1700 1144 14-1 15,111 (I l) 2% 1V" Feed 5 1'4 ('H,.h'i1|nce hydrogen (nmlu'7r 1; carrier. lllll'l hyillogcn comes in with steam "Pressure drop me at is (like a measure of degree of coking Wh flow and temperature data are not shown. these data were not recorded at the specific time tnlullntcil; howcvcr data tlimcs shortly before and alter the time tabulated. indicate that these conditions did not change during the time interval.

TABLE 4.-lR()DU(. '1 GAS ANALYSIS [Mole percent] Analysis with Analysis with carrier hydrogen carrier hydrogen included excluded based only on Iced Example Sample. 11: C0 011 C2116 C 11 C 11 113 CO 011 (3 11a C211 C 11 ()0 (.34: (a ((1 Ya 2th." 10-3 87. 20 0. 37 (3. 56 0. 00 0. 23 5. G5 81. 85 0. 52 .1. 31 0. (l0 0. 32 8. 0O 67. 55 .2. 24 55. 81 1. 80 82. 61 13-3 85. 84 0. 36 7. 24 0. 00 (l. .21 5. 81. 2'.) 0. 51 10. 2'.) 0. (l0 0. 31 7. [i0 t'rl. .Z 11 52. 52 1. 77 81. 41)

21) 14-3 87.136 0. 23 6. 06 ll. 00 O. 23 5. 81 82. 52 0. 31. 8. 5.) U. 01) 0. 33 8. .34 (31). JG .2. 313 57. 5'.) 1. 13 .3. 31 2C 14-4 84. 08 0. 32 5. 84 0. 01) (l. 21) J. 48 84. 01 ll. 32 5. 84 0. 00 U. 21) El. 48 72!. 06 .5. 11 58. 02 1. 14 86. 03

3:1 10-1 80. 21! 0. 34 3. 00 0. O0 0. 20 5. L" 84. 11 0. (i. 38 (1.110 O. 33 8.112 77. 13 1!. 35 (i1. 81 2. 01 80.18 13-1 811. 38 0. 47 4. 54 0. 00 U. 11) 5. 42 83. 51 0. 73 7. 05 0. 0t) 0. 30 8. 42 74. 8(1 2. 14 (i0. 17 2. (i0 80. 44 14-1 88. (10 0.53 6. 82 0. [)0 0. 2O 4. 45 81. 10 0. 83 10. 74 U. 00 0. 32 7. 01 (i2. 83 2.111 48. 4') :2. 88 77. 18

3b 10-1 90. 58 0. 28 2. 4!) (1.00 0.111 6. 45 85. 4!) 0. 43 3. 84 0. 00 0. 21] 1.115 85.113 2. 14 72. 73 1. 5.) 84. 87 3c 13-4 86. 51 O. 31 3. 33 0. 0O 0. 28 J. 57 86. 51 0. 31 3. 33 (l. 00 O. :38 l. 57 87. 75 2. 0'.) 70. 3'2 1. 15 801 13 421 13-3 87. 31 0. 45 (i. 65 0. 00 0. 24 5. 36 81. 21 0. 87 9. 88 0. 0O 0. 35 7. 93 65. 76 l. 43 55.18 2. 32 83. 00 14-3 86. 0. 58 7. 03 0. 00 0. 23 5. 30 80. 43 0. 87 10. 47 0. 00 0. 34 7. 89 63. 67 2. 36 54. 77 3. 01 811. 02

4b 13-4 88. 77 0. 28 4. 82 0 .00 0. 24 5. J6 83. 5O 0. 2') 7. 08 0. 00 O. 36 8. 77 74. J1 2. 52 62. 11 1. 04 82. 92 4c 14-4 84. 96 0. 32 5.10 0.90 0. 13 J. 41) 84. U6 0. 32 5. 10 0.00 O. 13 J. 4'.) 81. 56 0. 9G 68. 67 1. 17 84. 20

What is claimed is: l. A process for the control of coke produced in hydrocarbon pyrolysis reactors wherein hydrocarbons undergo pyrolysis to acetylene containing pyrolysis products, by injection of a supplementary gas stream selected from the group consisting of hydrogen, steam and mixtures thereof, said gas stream being at a temperature above 750C. but lower than the temperature of the pyrolysis products at the location of injection into the reactor system at a location downstream from that at which substantially all the pyrolysis reaction has been completed but prior to the point at which the said pyrolysis products are quenched.

2. The process according to claim 1 wherein the gas injected. is steam.

3. The process according to claim 1 wherein the gas injected is hydrogen.

4. The process according to claim 1 wherein the gas injected is a mixture of steam and hydrogen...

5. The process according to claim 1. wherein the gas stream is injected at a location between that point at which the maximum reactor profile temperature occurs and that point at which sheet coke forms under conventional operating conditions.

6. In a process for pyrolysis of hydrocarbons to acetylene, the improvement which comprisesinjection of a 55 supplementary gas stream selected from the group consisting of hydrogen, steam, and mixtures thereof, into the reactor at a location downstream from, that at which substantially all the pyrolysis reaction has been completed but prior to the point of quenching whereby 60 production of coke is controlled and the duration of the,

feed inlet, and is allowed to flow through the pyrolysis reactor until coke is removed from the entire reactor and then re-cstablishing the original feed and supplementary gas stream flow pattern.

11. The process of claim wherein the feed stream to the reactor is interrupted prior to diverting the supplementary gas stream.

12. The process of claim 7, wherein after overall reactor coking occurs, at least part of the supplementary

Claims

1. A PROCESS FOR THE CONTROL OF COKE PRODUCED IN HYDROCARBON PYROLYSIS REACTORS WHEREIN HYDROCARBONS UNDERGO PYROLYSIS TO ACETYLENE CONTAINING PYROLYSIS PRODUCTS, BY INJECTION OF A SUPPLEMENTARY GAS STREAM SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, STEAM AND MIXTURES THEREOF, SAID GAS STREAM BEING AT A TEMPERATURE ABOVE 750*C. BUT LOWER THAN THE TEMPERATURE OF THE PYROLYSIS PRODUCTS AT THE LOCATION OF INJECTION INTO THE REACTOR SYSTEM AT A LOCATION DOWNSTREAM FROM THAT AT WHICH SUBSTANTIALLY ALL THE PYROLYSIS REACTION HAS BEEN COMPLETED BUT PRIOR TO THE POINT AT WHICH THE SAID PYROLYSIS PRODUCTS ARE QUENCHED.

2. The process according to claim 1 wherein the gas injected is steam.

3. The process according to claim 1 wherein the gas injected is hydrogen.

4. The process according to claim 1 wherein the gas injected is a mixture of steam and hydrogen.

5. The process according to claim 1 wherein the gas stream is injected at a location between that point at which the maximum reactor profile temperature occurs and that point at which ''''sheet coke'''' forms under conventional operating conditions.

6. In a process for pyrolysis of hydrocarbons to acetylene, the improvement which comprises injection of a supplementary gas stream selected from the group consisting of hydrogen, steam, and mixtures thereof, into the reactor at a location downstrEam from that at which substantially all the pyrolysis reaction has been completed but prior to the point of quenching whereby production of coke is controlled and the duration of the pyrolysis cycle is increased.

7. The improvement of claim 6 in which the supplementary stream is steam.

8. The improvement of claim 6 in which the supplementary stream is hydrogen.

9. The improvement of claim 6 in which the supplementary stream is a mixture of steam and hydrogen.

10. The process of claim 1 wherein after overall reactor coking occurs, at least a portion of the said supplementary gas stream is diverted to the pyrolysis reactor feed inlet, and is allowed to flow through the pyrolysis reactor until coke is removed from the entire reactor and then re-establishing the original feed and supplementary gas stream flow pattern.

11. The process of claim 10 wherein the feed stream to the reactor is interrupted prior to diverting the supplementary gas stream.

12. The process of claim 7, wherein after overall reactor coking occurs, at least part of the supplementary gas stream is diverted to the reactor inlet, and is allowed to flow until coke is removed from the entire reactor followed by re-establishment of the original feed flow pattern.

13. The process of claim 12 wherein the feed stream to the reactor is interrupted prior to diverting the supplementary gas stream.