US2236535A - Manufacture of acetylene - Google Patents

Description

R. 1.. HASCHE ,535

MANUFACTURE OF ACETYLENE Fild July 10, 1957 2 Sheets-Sheet 1 INYENTOR.

udolph Leonard Hascbe April 1, 1941.

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MANUFACTURE OF ACETYLENE Filed July 1.0, 1937 2 Sheets-Sheet 2 FIGZ. FIG .4.

102 FIG .5.

I400 FIG. 6.

Hf 1 T HEUIREZI? FOR IEED I I I I I200 BA ICE BUTA E AT D N 8-! I I I I I000 I I I 800 1 L TE Q: 600 F! E "M a:

W. It 200 L PER 23? 400 600 800 /000 1200 /400 BIU. REQUIRED TUBE TREVERSED Z0 40 Rudolph Leonard Hasche Patented Apr. 1, 1941 7 2,236,535 I MANUFACTURE OF ACETYLENE Rudolph Leonard Has che, Kingsport, Tenn, as

signor,

by 'mesne assignments, to Wulfl Process Company, Los Angeles, Calif., a corporation of California (I i Application July 10, 1937, Serial No. 153,044 9 Claims. (Cl. 260-679) This invention relates to a process of making acetylene, or a gas containing acetylene, together with numerous by-products to be named and characterized herein. More particularly it relates to a pyrolysis process for making acetylene more economically than has heretofore been known.

, Various processes for the manufacture of acetylene are shown in the several Wulfi patents, for example, 1,880,308 and 1,880,309. My process is similar to the processes described in the Wulif patents in a number of respects. However, my process constitutes an improvement thereover as will be apparent as the description proceeds.

This invention has for one object to provide a "method of producing maximum yields of acetylene from each unit of raw hydrocarbon to be processed. Still another object is to provide a pyrolysis process which permits the use of a' variety of proportions of diluent. A' still further Object-is to provide a pyrolysis process in which there is a special preheating before final pyrolysis, thus producing improved performance and increased capacity. A still further object is to provide a high temperature pyrolysis process in which there is a definite relationship between the heating surfaces and volume heated. A still further object is to provide a high temperature pyrolysis process in which there is definite expansion ratio between the materials pyrolyzed and the products obtained.

Still another object is to provide a pyrolysis process in which there may be reuse of a chosen part of the products which have been previously formed therein. Another object is to provide a high temperature process for the production of acetylenic hydrocarbons from raw materials which may contain more or less sulphur components. A still further object is to provide a process for producing acetylenic and oleflnic hydrocarbons in equipment which may be comprised in part of nickel. Other objects will appear hereinafter.

I have found from extensive investigation of a number of factors of operation, wherein increased economy of operation and other advantages may be obtained. As indicated above, the several Wulif patents disclose processes of acetylene manufacture. These patents set forth various details such as a number of different type hydrocarbons that may be converted to acetylene, a number of difierent diluents that may be employed, temperatures, pressures, details relative to rapid cooling and a number of other factors. These patents also show suitable apparatus.

Since these and other details are already available, it appears unnecessary herein to repeat such information, hence, on certain features discussed herein only brief references are made. While any suitable apparatus may be employed for carrying out my invention, certain apparatus shown in the Wulif patents being satisfactory, Iprefer to employ an-apparatus arrangement as shown herein.

For a more complete understanding of my invention, reference is made to the attached drawings in which Fig. l is a. diagrammatic representation in the nature of a flow sheet of one apparatus set-up for carrying out my invention. Figs. 2 and 4 are side elevation views of fillers or corebusters which may be contained in my pyrolysis tube. Figs. 3 and 5 are end views respectively, of aforementioned corebusters. Fig. 6 is a chart showing a heating relationship, with particular reference to my preheating ste In Fig. 1, the primary stock to be used in making acetylene and other products, is supplied from the container I. In the line 2 may be a valve 3 for regulating the rate of ,flow. Following valve 3 is a flow meter 4, followed in turn by a heater 5. The heater 5 may operate in the conventional manner by admitting at l a heating medium about the tube 6. At the pipe juncture ii the primary stock joins with diluent furnished through the pipe l2. Valve it serves to adjust the rate of now of the diluent, and i4 is a flow meter in the line. The pipe may also make communication with the point of juncture H for admitting secondary stock in a manner to be described.

Pipe l5 carries the feed to the preheater It;

This preheater comprises a housing 38 and a heating coil i! that receives the feed from pipe IS. The heating medium for the feed in coil I! may be flue gas in countercurrent, coming from the cracking furnace 42 operating in conjunction. Flue gases forming in the combustion chamber 83 of the said furnace, pass into a duct 65, and may be manipulated such as by the two dampers 3| and 40, to serve as mean for controlling the degree of preheat in coil I1. From the coil l'l the feed passes into the pipe IS, in which there may be a chamber as at 86. Integral therewith may be a thermocouple well 61, where the degree of preheat of the feed may be determined by the thermocouple 8| indicating at the pyrometer 82. If a chamber is not desired, then the thermocouple well may be integral with the pipe l9 which leads directly to the trap 20. .The purpose of this trap is to catch any oils and tars that form from the feed at times due to the action of the tailed description appears unnecessary.

preheater it. Any accumulation in trap 2G may be drained at will through valve 2!,

The preheater is connected through pipe 22, to

the cracking tube 2% through a fitting 23. The cracking tube 24 may be heated by one or more burners as at 25, supplied with fuel and air respectively through valves 26 and 21. Preferably there are at least two such burners, disposed to give the most uniform possible heating of the said tube. Cracked mixture leaves the tube 2%, passes through a fitting 29, and enters pipes ill), M, and 15 which convey it to the quencherd3, which it enters at a point 32. The said pipes 30, id and 15 are preferably water-jacketed or otherwise cooled, while in fact both fittings 23 and 29 are of cooleddesign, for purposes to be brought out in full later. 79 indicates a point of entry for a thermocouple "it used for testing at different levels within the tube 2d, temperatures indicated on the pyrometer ll.

While I have indicated the use of temperaturemeasuring instruments; flow meters and the like, at Various points in my apparatus, it is to be understood that my invention is not limited to such construction or use of such instruments and various :other instruments may be employed or attached to my apparatus at difierent points.

The quencher it is preferably a tower fitted with liquid connections such as 3%, 35, and 33, each of these having a valve as indicated for adjustment, and a spray device 66 within the tower in operating relation to the said liquid connection and valve. The cracked mixture, cooled by the pipe 30, on entering tower 13, at 32, is suddenly chilled by the water or other liquid sprays within, to a temperature at which acetylene and ethylene are stable. At the same time the diluent, if of boiling point substantially higher than that of the final gas temperature in the tower, will for the most part be condensed. Together with such diluent, will be removed from the cracked mixture, the greater part of any oil and asphalt or tar vapors, particles of solid organic matter, and particles of carbon that the said mixture contains as a result of the cracking operation in tube 2d. Such material removed from the gas, for the most part is liquid, making possible its removal from the tower at will, through the trap 6 5.

At a point 33, the unit 53 is connected to filters 3i, 3? and oil scrubber 86. The oil scrubber 88 is connected to the suction end of the pump w, whose full function is to be explained later. it is a valve for by-passing part of the discharge of pump-B9. The said valve H is operated by pressures in chambers 23 and 63 communicating through pipes i2 and i3, respectively. The purpose of this valve ii is to maintain a desired ratio between the pressures in the chambers 23 and 83. The exit end of the pump 69, is connected to a meter 6, a gas holder 85, and then preferably to a dryer 65.

It should be repeated that Fig. 1 does not show each of the units of the process in its exact form, but diagrammatically. More particularly is this true of unit 48. The unit 38 is interconnected with the system at points M and 55. These units may be in the nature of scrubbing towers, extractors or other construction employed in the art for recovering and separating acetylene and ethylene. Inasmuch as a number of constructions for recovering and separating acetylene and ethylene are shown in the art, further de- It is to be noted in passing, however, that some arrangement may be employed wherein medium employed in unit 68 may be conducted thereupon and fed to parts 33, 85, and 36 through conduit 9!. The stripped gas may be removed as at 62.

In any event the acetylene produced in my process may be separated as at 68 or reacted, and the ethylene or other olefine produced likewise separated and conducted to conduit 53.

Figs. 2-5 show construction which may be contained in my pyrolysis tube 2%. This construction serves to improve the pyrolysis process by facilitating heat transfer as Well as (in cooperation with tube 24) of producing a definite area ratio within the pyrolysis chamber. Construction may be of a number of types, for example, one type of corebuster may comprise a cylindrical refractory unit mi. This unit will have positioned on it at various points, lugs me which serves to more or less center the corebuster within the device. Channel 503 is for the reception of a pyrometer unit or other mechanism. If desired, a construction such as shown in Figs. 4 and 5 may be employed. This construction includes a refractory unit W6 having thereon the protrusions lfl'l which serve to position the corebuster within the pyrolysis tube. In general, this modification is more or less of a star-shaped design and as already pointed out, may contain a passageway Hill for the reception of temperature-recording instruments.

The operation of my process with variations, is preferably carried out in the following manner, reference being had to the accompanying drawings, principally Fig. 1. The various mechanism in my apparatus would be set in operation. Thatv is, fuel and air pressure would be supplied to the burners, filter material, oil scrubbing medium and cooling medium would be supplied to the various parts. The pyrolysis tube and preheater would be heated. The various spray valves 36, 35 and 36 are open while quenching agent flows out through trap M. The valve 1! would be adjusted so that the pressure exterior of pyrolysis unit 26 would be about equal to the pressure in the interior thereof (or at some other predetermined relationship) for minimizing leakage or controlling or inducing leakage in a particular direction. Steam or other diluent material, such as shown in the Wulff patents, may be allowed to proceed from the valve it. When the ap paratus has obtained the desired temperature, material to be pyrolysed may beied in from container 1 through the various conduits. Heat may be applied at 6 if desired, for vaporizing the material which is to be pyrolysed. The proper proportions of materials, of course, may be obtained by regulation of the valves and notation of the flow through the respective meters. Any materials condensed in the preheater may be removed from trap 28 through valve 2i.

I prefer to operate at a high temperature of preheat within a particular range, and dampers 3| and id are accordingly adjusted to this end. My high temperature of preheat is desirable. since I have found that if the temperature in metallic tubes, such as the coil H, is properly applied the greater can be the per hour capacity of the pyrolysing tube 24, which may not so easily pass heat as a metallic tube, and which also is more expensive and less durable. In short, while .my process forms acetylene at so high a temperature as usually to require a refractory tube in the final treatment, still much of the load of heating can be taken off the said tube through the use of the proper preheat in less expensive equipment. Further than that, I find that the changes that occur in the feed as a result of the preheating, can be very beneficial if. they are controlled. In other words, certain reactions possible in the feed during preheat are useful, and others are not. It is therefore a part of my invention to single out such reactions as are useful, and permit them to occur alone or predominately during preheating of the feed, and to such an extent as conduces to the economy of my process.

Reference is now made to Fig. 6 which is a graph that illustrates one of the advantages of my method of preheating. The curve gives. the B. t. u. value required to heat one cubic foot of butane diluted with eight cubic feet of steam. Up to 600 C., the curve is steep, since the only need of heat is due to specific heat. From above 600 C. the curve is much less steep, due to considerable demand for endothermic heat. I have found, therefore, that to preheat at above 775 to 800 C., namely, above the point where endothermic heat is required, materially alleviates the load on the pyrolysing step. Attention is called to the fact that the curve shown in Fig. 6 represents butane at a steam dilution of eight volumes per volume of butane. In my process, I may dilute with as little as 3 volumes of steam to l of butane. In such cases, it is evident that the endothermic heat is then a much larger proportion of the total heat required by the feed in the preheater. Thus it becomes part of my invention to preheat above 750 C. and generally above 800 C.

For a still further understanding of my preheating step, reference is made to the following table showing a series of tests carried out with normal butane at a dilution of eight in a tube of about .546 inch internal diameter, containing a corebuster of .375 inch outside diameter. The rate of flow of steam used as diluent was .222 and the rate of fiowof butane was .208 c. f. m. The time of passage was, of course, extremely rapid and the residence period of the materials in the tube was substantially less than 116 of a second.

Percent by weight of N-butane converted to various products The aforementioned table shows plainly that from the standpoint of economy of raw material ordinarily 1000 C. is a better temperature than lower or higher temperatures, since the total of olefines is at a maximum there. Attention is called however, to the larger proportion of butane converted to carbon monoxide at higher temperatures, which no doubt accounts for the disappearance of some olefines.

Care is taken herewith to point out that the term expansion in the ,aforementioned table is applied to fixed gas in the feed; after preheating rather than to cracked gas as above defined.

The results in the aforementioned table show that different temperatures may be employed .to secure somewhat different decomposition products. One may work to a maximum volume concentration of oleflne plus acetylene or to a maximum percent by weight conversion of raw materials ito olefine. It is to be understood that the 1000 C. which I desecribe as the optimumtemperature of preheat is not altogether inflexible but, of course, depends upon factors such as the particular raw material used, the length of time that the feed is subjected to preheating, and the temperature of preheat. In general, for longer periods of preheating, the temperature should be lower than 1000 C. whereas for a short period the temperature might be somewhat higher. all instances, however, the time of preheating is preferred to be kept to a low value, under a few seconds, preferably considerably under one second. The upper limit of the temperature of preheat is conditioned, however, largely by the disappearance of olefines due to carbon monoxide in excessive amounts. In other words, I do not wish to preheat at such a high temperature or for such a long period that materials being preheated or formed during my preheating would become converted to carbon monoxide or'other non-useful components. When I have reached the temperature in the preheating wherein the olefine component is disappearing, due to the formation of carbon monoxide, I conducted the preheated materials to the .tube 24 of Fig, 1. In this tube high temperatures may be employed, while yet controlling the quantity of carbon monoin'de formed. This is due to the selection of materials such as carborundum or other refracrtory to .the cracking tube wall, combined with a brief period of residence in the same tube.

Therefore, the feed, thus preheated in the coil i1, and whether or not modified in chemical con stitution thereby, proceeds then to the fitting 23, which is now already hot and does not condense diluent. From there it courses through the cracking tube 24 where is formed a substantial amount of acetylene.

- Feed having been cracked in the tube 24, then becomes a mixture of cracked primary stock and diluent, including by-products of such cracking as for instance organic condensation products and carbon. Included in the said mixture are any products of reaction of diluent with the primary stock or with any of the products it forms in the tube 24. This mixture of gas as described in .the present paragraph has been termed cracked mixture, and will so be called herein. And while the mixture is given this name, it is nevertheless to be understood that there will be a certain amount of physical and chemical change in the mixture between the point that it leaves the tube 24 and enters the quencher 43 which fixes its composition. The said path is waterjacketed or otherwise cooled (as with refrigerants) to chill the cracked mixture as rapidly as possible from the instant of exit from the tube 24. To this end even the fitting 29 may be Waterjacketed. I therefore drop the temperature of [the cracked mixture instantly to any predetermined point more or less in accordance with the teaching of the Wulfl patents aforementioned.

' The products treated in unit 43 are clarified, cooled and purified to some extent. However, the filters 31 and scrubber 86 remove carbon particles, oils and any other materials contaminating the cracked products.

After leaving .the scrubber 86, the cracked gas is picked up by pump 69. The adjustment oi the stud 16 on .the by-.pass valve H is now made so as to hold about the same pressure within chamber 23 as within the combustion zone 83. Valve H of course performs this function by varying suction on the pump 69 through the bypass line in which it operates. Higher or lower pressure may also be produced.

After the pyrolysis has continued for a short period recirculation may be set up. To this end are opened valves 83, 62, 51, and 6t, and the pump 84 is set in operation. "Then valve 80 is manipulated to force cracked gas into the gas holder 85, and adjusted so as to hold the gas holder always partly full. Then valve 8 is opened .to cause a flow of gases through the unit or units designated at $8 and valve 8b is again adjusted to maintain a quantity of gas in the gas holder 85. Valve 6% is then further opened, increasing the flow' of gases in til. These operations with valves 5d and 80 are repeated rtill at last valve 8!) is closed, and valve M is open at a point that will still hold a quantity of gas in the gas holder 85. According to the actual manner of operation of 48, these are set in action and adjusted till satisfactory results are evident from .the purity of ethylene and acetylene isuing.

thereupon and from the. leanness of stripped gas issuing from the valve 62. At this point I may recirculate ethylene by opening valve 9 so it will mix with diluent and primary stock from container l as before described. As valve his then 0 admitting ethylene (or other secondary stock) to the system for recirculation, valve 65 is adjusted to relieve only what ethylene is not passed through the said valve 9, for otherwise the process of separation may be disturbed, or the purity of .the ethylene may drop. And if all the ethylene produced is recirculated in this manner, then obviously valve 6t should be closed. It will also be obvious from Fig. 1 that the pump 85 of need would have a delivery pressure convenient to the niceties of control as to recirculation and sufficient to exceed easily the pressure in the pipe juncture H where the mixing is to take place.

In the material immediately foregoing, the separation of acetylene from the cracked gas is described as carried out in a unit or units designated 38. And it is herewith repeated that the system of separation is only illustrative. Any

of a number of methods may be employed. The

separated product may well include more or less of the material to be found in my cracked gas. Hence, in the following matter reference will be had largely to secondary stock rather than ethylene as secondary stock.

Such diluent as may have been of boiling point too low to be condensed in the quencher 13, will pass out of the separation system still in the stripped gas leaving the point 62 of the tower d3. According to the type of diluent, it may be removed from the said stripped gas in ways known to the art, either for increasing the value of the stripped gas, or for recovery of the diluent as in repeated use. If the stripped gas also contains acetylene at the said point of exit 62 of the tower d8, of course that tools recovered for use as may be desired. Thestrlpped gas resulting may very well be used as fuel for firing the cracking furnace t2, as I elect to do, for reasons to be pointed out hereinafter.

When recirculating ethylene, or olefins generally, I may secure a higher content of acetylene in the resulting gas than before, as well as a higher yield. Also, I may have a higher content of ethylene, due to the fact that ethylene survives the heat treatment in the cracking tube of temperature herein. v

steam used for dilution, are all measured inassesses standard cubic feet, and ratesof flow in cubic feet per minute, for convenience abbreviated c. f. and c. i. m. So for all primary and secondary stock and any diluent herein, a standard cubic foot of gas represents the quantity of gas in such a volume at 25 C. and one atmosphere absolute pressure, and will so be understood herein. The weight of such a volume of a given gas or gas mixture, is assumed to be equal to the molecular weight; or average molecular weight, in pounds, divided by 384. And while steam is of course non-existent in those conditions, still the hypc= thetical volume is herein computed by extrapolation as though it did exist, and behaved like a fixed gas such as nitrogen. In order to establhh without possible doubt the meaning of one standard cubic foot of steam, it will be assumed herein that such a unit of steam weighs 18/384=0.0d68 pound avoirdupois, arrived at exactly as for gases. The same formula is herein to be applied to other diluents and other normally liquid substances according to their molecular weights. The care'exercised in this paragraph in establishing units and factors of conversion is for eliminating any possible confusion, and to the fact that for purposes of test ing variables relating to my process, 'it is better to speak in terms of volumes rather than weights, while for purposes of elucidating economies, the converse practice is more convenient.

The item Dil." signifies dilution or extent of dilution, expressed as the ratio of rate of flow of diluent to that of stock being cracked, each expressed in c. f. m. The itemFExp." signifies expansion or the number of cubic feet of cracked gas formed with one cubic foot of stock cracked. Gas analysis is given in percent by volume. Conventions developed in this paragraph will be used throughout herein, except that Exp." in preheater tests may at times refer to fixed gas resulting from preheating rather than to cracked gas, as will be clear in context.

Ratio of surface to volume will be expressed in square feet per cubic foot. For instance, in a preheater tube of 1.75 inches internal diameter, without corebuster, the said ratio is If a corebuster is present, the sum of the internal areas exposed to the stream, is divided by the net volume bounded by said areas. If the corebuster is cylindrical, the volume is then annular. If the outer surface of the corebuster has a special shape, the area of that surface is estimated for use as above.

Ratio of area to volume, hereinafter to be termed area ratio, in the preheater tube may range from as much as 250 to as little as 5. if have found that the range permissible here is very wide, since it may be compensated not only with temperature, but also with residence period. For the higher the area ratio, the more rapidly the gas will absorb heat, and the less severe the temperature needbe, or the less the period 7 2,286,535 of heating. Wide fluctuation of area ratio brings wide fluctuation of residence period, but not such -a great variation oftemperature. Hence, the

temperature range remains nevertheless rather well fixed. All. the more. however, is the emphasis'oi' gauging extent of preheat by the expansion as above defined out in more detail.

Dilution has little influence ,on results that may be secured in preheating, so long as the preheater is designed to take care of the heat transfer requirements that arise. Dilution will thus be kept for discussion under the cracking stage.

In addition to preheating as described above, and thereby obtaining improved yields, I have found several other features which may be applied in my process for the manufacture of acetylene withthe resultant production of still further improved yields. I t-is understood, however, that these various steps to be described, while preferred, are to some extent optional. Hence, one or more or a combination of the fol-=- lowingfeatures may be utilized.

I have found that if the feed materials, such as my primary or secondary stock, contain appreciable portions of sulphur in the form of hydrogen sulphide or other volatile sulphur compounds such as light mercaptans or organic sulphides, the yield of acetylene as well as ethylene or other olefines is diminished thereby. For further illustrating this point, reference is made to Tables 1, 2 and 3. In Table 1 is shown a composition of a gas containing hydrogen sulphide. It is, of course, understood that this is illustrative and gases encountered might contain more or less volatil sulphur materials.

TABLE 1 'Firom-a comparison of Tables 2 and 3, it will beobserved that aggregate yields of acetylene and olefines may be considerably improved if sulphur is absent. In the example of Table 3 the hydrogen sulphide was removed from the gas by treat ment with a caustic soda solution in a conventional manner. Cracking was carried out in the equipment already described. It is also evident firom Tables 2 and 3 that .there is greater expansion due to the presence of sulphur. Further computations will show that the additional carbon monoxide formed, due to the presence of suland'as will be pointed phur, may probably be accounted for by the decrease in acetylene and ethylene.

Therefore. the net result of the presence of sulphur and particularly too great a content of sulphur in the materials to be pyrolyzed', is to reduce yields. It is therefore a pant of my invention to provide against this difficulty, inasmuch as a great amount of raw material (such as the composition shown in Table 1) is available for use in my process. It is, of course, possible, as already indicated, to remove sulphur from the stock before subjecting it .to treatment. There are a number of processes known for removing sulphur and I may apply any one of these processes to my stock before conducting it through the apparatus.

I have also found that it is possible to use such a stock which contains sulphur by substituting or complementing [the treatment for removing sulphur, with a partial or total substitution of any steam diluents supplied to the feed. Another more nearly inert diluent or a suitable equivalent of re duced pressure or both of these expedients may be employed. I have discovered that sulphur in conjunction with steam is a factor tending to destroy .the acetylene and ethylene which I wish to produce. Hence, I disclose the utility of operating with less sulphur, or if sulphur is present, less steam in the presence thereof or with less of each. In closing this point, it is desired to bring out that this feature has considerable utility because of the availability of large quantities of sulphur-containing gases which may be treated by my process.

Referring again to the preheater construction, it is preferred to use any of the various heatresisting alloy steels such as chromium steels, chrome aluminum, chrome molybdenum or chrome tungsten steels. However, there ace various other heart-resisting alloys such as chrome nickel alloys, chrome nickel steels and the like. In operating my process in som instances such as with previously constructed apparatus, the occasion may arise wherein the preheater tubes are constructed of materials containing more or less nickel. I have found in such instances that improved operation may be obtained by using less steam as a diluent, substituting therefor, a more nearly inert diluent if not also a certain measure of reduced pressure. Under some conditions I may also elect to use preheater apparatus containing a moderate content of nickel together with less steam and an inert diluent or a measure of reduced pressure. I may also counteract undesired reactions by introducing into the feed a substantial part of any steam diluent, or other diluent which may with a particular preheater or feed produce difficulties, immediately after the preheat rather than as above described.

From the preceding it is apparent that I have set forth a process which may be applied not only to high-grade stock, but also to less desirable stock which may contain splphur. It is also apparent that I have provided a process which may be operated in apparatus constructed of any of the various metals and alloys usually ncountered in the industry.

With further reference to my novel preheating step the exact temperature of preheat in a suit-able tube and with a suitable diluent, already has been stated to depend to some extent on the period of heating employed. It should also be made clear that this temperature is dependent also on the nature of the raw material used, being toward the higher values for raw materials of lower molecular weight. It the temperature is to be .the same, then the period of heating should be somewhat longer with raw materials-oi lower molecular weight. In general, I prefer also to use slightly less dilution with raw materials of low molecular weight, excepting in the case of methane. For, in the case of methane, I have found that with a preheating temperature of from about 900 C. to 1100" C. and a period of heating suited to whether a higher or lower temperature is chmen, there can be secured under sufllcient dilution, particularly with steam, a considerable conversion of methane by the preheating step. Such a change in the preheating step probably constitutes an actual synthesis requiring the union 01! two molecules of methane or rather of their two ca-nbon atoms. This is of considerabl importance in the formation of acetylene, inasmuch as it will be noted that acetylene is a two-carbon atom molecule, whereas methane has but a single carbon atom. By being able to convert apart of the methane to a heavier molecule by means of my preheating step, it is apparent that the formation of acetylene therefrom in the cracking step is also facilitated.

I prefer to preheat longer and use higher dilutions with methane than with other raw materials. However, I prefer the same approximate final temperature of preheat (namely, around 1000 C.) in order that the end products in every case may be similar. The period of residence in the preheater should be the same as with my other raw materials. That is to say, when acetylene' begins to appear in my preheater on feed containing methane as a raw material, I would elect to speed the feed through its final stages in the same manner as has been described in reference to butane and other raw materials.

Having referred specifically to the case of methane as against other raw materials in the operation of my process, I may elect to make use of reaction chamber 66 in the line it (see Fig. 1). This reaction chamber would receive feed that has already reached the temperature at which methane or other materials are becoming converted to heavy molecules such as the olefines, and holding it until all such olefines have formed. The period of time, of course, would be dependent upon the internal volume of the reaction chamber in comparison to the rate of flow of feed. It is understood, however, that the chamber is placed in the preheater coil at a point preceding that at which acetylene forms, for it is the purpose of said reaction chamber to give time, for example, for ethylene to form, whereas for forming acetylene no large time element is necessary.

It bears emphasizing that those skilled in the art will agree as to the difiiculties presented when attempting to determine true gas temperatures for purposes such as relate to my process. I emphasize also, therefore, that when I report, discuss, or choose temperatures, these are measured and chosen for what they may actually be, and not necessarily as being exactly what they were intended or hoped to be. But being temperatures measured in a definite specified manner, those skilled can duplicate experiments on the basis of such guidance, and secure similar results to those I report herein.

Thus for these and other reasons given, it is not possible to determine with finality the actual length of time of heating of a gas in stream. Past statements in the literature relating to the said period of heating have, however, been particularly nebulous arbitrary, hence, I propose to estimate them only on the basis of iully detailed specifications of experiments, and fully clarified of elements of error and uncertainty.

Hereinafter the said period of heating will be termed residence period, and will be understood to be the length of time in seconds that a given portion of gas, whether in stream or static, is undergoing a particular unit heat treatment, re-

mains in the unit giving that treatment. For

instance, the residence period for feed bein D heated in the preheater 16 of Fig. 1, is that number of seconds during which an element of the feed remains inthe coil H or the coil I'I plus the reaction chamber 66 as the case may be.

If preheatingof the feed is carried out without a reaction chamber such as may be desired for methane, the temperature rise of the feed during its passage through the preheater tube will be nearly proportional to the length of tube traversed, particularly if heating is uniformly countercurrent as is common practice. The graph in Fig. 6, however, shows how the feed temperature suffers retarding in this respect, toward 600 C. due to the endothermic heat requirement discussed.

In general, the feed enters the preheater at about 100 C. and one atmosphere absolute pressure, that is, zero gauge pressure. At times, I may wish to use higher temperatures and pressures, as for instance if I wish to speed the feed through the preheater, or again if I desire to maintain an appreciable gauge pressure at the inlet end of the cracking tube. Indeed, it is my practice to hold a few pounds of gauge pressure at the inlet to the preheater tube, in order to hold the feed in flow and still hold zero gauge pressure at the inlet to the cracking tube. It will 'be assumed, however, for practical purposes, that the feed enters the preheater tube at 100 C. Since also I may preheat up to 1000 (3., the graph of Fig. 6 has been constructed to represent this rise in temperature along the length of preheater tube, in which the feed has residence. Though it is clear that the temperature is not strictly a straight-line function of the distance passed, such will nevertheless be assumed.

Thus, if there were only the natural thermal gaseous expansion of the feed in traversing the preheater tube, as there would be with a gas such as nitrogen, similarly passing through, one would arrive at the residence period by considering the internal volume of the said tube in realtion to rate of flow and average temperature, say at zero gauge pressure. This I propose to do, neglecting the unavoidable expansion due to chemical dc composition of the raw material. For the pertinence of a correction due to this factor is very doubtful in view of the question as to the temperature distribution of such expansion. I recognize further that this error is not constant, but dependent on the extent of expansion, as well as on the dilution. For with less dilution the raw material occupies a larger proportion of the total feed volume, and therefore the expansion causes a greater error in estimation of residence period.

Thus simplified, the method oi? computation may be illustrated to remove all doubt of proce dure and definition. With 12 c. i. m. of butane and 96 c. f. m. of steam as diluent, the total rate of flow is 108 c. f. m. If the temperature of the preheater on the average is an average between 100 and 1000 0., then the average rate of flow effectualis .r' gg gg 103:304 cubic feet per mimlte of thermally expanded feed. Then if the preheater tube volume is 2.66 c. 1., the time of heating will be r 304 0.00870 minute or 0.5 second, in which more than one significant figure is not Justified due to uncertainties and simplifications. e

Having now covered substantially my disclosures on preheating as a step in my process, I proceed to give the operating and preferred ranges of values of variables that determine the results of preheating.

I prefer to preheat as high above 800 C. as possible, being limited largely by excessive formation of carbon monoxide, which as has been shown, is a variable factor. With good equipment in conjunction with expedients of operation herein set forth, I prefer to carry preheat up to 950 C. and beyond when possible, to include some acetylene formation if possible. As a general thing, however, I prefer to preheat from 850 to 900 C., realizing that the actual temperature which is best to use, depends on the residence period, and on practical limitations such as heat-resistance of alloys available for construction of preheater.

Residence period may well range between 0.1

and 4.0 seconds, for raw materials except methane, and may conveniently be 0.3 to 0.8 second for ordinary operation. Residence period with methane as raw material, may be from 1.0 to 5.0 seconds, depending on certain considerations, as

for example the conjunctional use of reduced pressure. The two sets of ranges here given of course are interrelated with the range of temperatures of the preceding paragraph. It will be seen that a slight alterationof temperature permits a rather wide variation of residence period.

Since temperature and residence period are so related and not independent, I prefer to introduce a third measure of extent of treatment, which is more directly indicative of whether the feed has received the proper thermal treatment. I find it strongly advisable to be guided, in preheating, by the expansion that results, that is, by the afore-defined ratio of volume of fixed gas formed to volume of raw material that forms it.

For either normal or isobutane, or for a mixture of them, I prefer to preheat until I have secured an expansion of from 2.0 to 3.5 wherein I allow for a reasonable amount of expansion due to car bon monoxide and water-gas hydrogen. Correcting for carbon monoxide, the range of exa pansion would be 2.0 to 3.2, while it may be said in general that 2.5 expansion is approximately the best in view of present-day limitations as to non-catalytic metals. And it is not be forgotten that raw materials of lighter molecular weight in turn have their own characteristic expansions by which I elect to judge optimum extent of preheat, while for the light olefines it is again slightly different. Thus for methane I prefer expansions of 1.1 to 1.4:, including small amounts of carbon monoxide, say of not over 5% by volume in the fixed gas. Expansion for ethane should be from 1.4 to 1.8, while that of propane should be 1.8 to 2.2. No expansion is required of ethylene, except for small amounts of acetylene formed, since it is of course itself a suitable raw material for the cracking operation. Expansion for propylene should be 1.5 to 1.9, and for butylene 1.8 to 2.2. These figures I use as a basis for determining the most advantageous expansion of raw material according to its chemconductivity and resistance to spalling may be used as wall material for my cracking tubes, I have preferred carborundum. The corebuster within the tube canbe mad-e of either of these materials, or of still others such as mullite, since the corebuster is not subject to quite such severe strains as the tube, and need not remain in such superior mechanical condition. Whatever the material of the corebuster, it must be such as not to slag down with the tube material. For atmospheric pressure work I prefer carborundum, although other materials are suitable.

While in carrynig out my process the tube shown in Fig. 1 at 24 may be of any suitable size,

r the purposes of illustration I describe my process as being carried out in a 4-inch internal diameter tube of about inch wall thickness. This tube may contain a cylindrical corebuster about 3 inches in diameter, thereby giving an area ratio of 96. If in place of using the cylindrical corebuster I should employ corebusters of the type shown in Figs. 4 and 5, I would be able to increase the area ratio to 200 and above.

If I assume for consideration of operating variables, a 4-inch tube of 7 inch wall thickness and a 6-foot length exposed to heating in the combustion chamber with a 3 inch cylindrical corebuster giving constant gas path section and a feed of butane and steam at a dilution of 8, I can more specifically illustrate my process. The feed would enter the cracking tube at about 900 C., preheat and at a preheater expansion of 2.5. It is understood that these, values are set forth merely for the purposes of illustrating my preferred embodiment and as apparent from disclosure herein, ma be varied and modified.

I find that for securing the optimum production in my process there should be obtained an expansion of from about 3 to 4.2 in the cracking tube. For further illustrating what has been said with respect'to expansion, reference is made to Table 4:

TABLE 4 Relation of butane expansion to yield Yield, vols. per 100 vols.

(1H4 Total While I have discovered that my process operates satisfactorily with dilutions as low as 3, such low dilution is not preferred, excepting in instances aforementioned, where the feed contains volatile sulphur or the preheater is constructed of certain metals, because such lower dilutions give more rapid accumulation of tar while providing excess -i'uel for the furnace. Hence, I

prefer and have found that dilutions from about to 8 and at times up to 18 when using a raw material containing only a small proportion of ethylene, are particularly satisfactory. As iridicated in the preceding disclosure, with respect to methane my process may be carried 'out in one of two directions. Either I convert in the preheater at dilutions from 20-40 thereby obtaining ethylene from the methane, after which the preheated feed is handled as ethylene-rich feed. Or, when treating methane I may use dilutions from about 3-6 together with a cracking temperature from 1300 C. to 1600 C. With respect to ethylene feed, preferably this should have expansion of about 1.7 to 2 ormore, while a temperature range 0! from 1150 to 1400 C. would be suitable. Methane should have an expansion of from about 1.4

to 2.2, while the temperatures required in the pyrolysis tube 20 would be higher than for other materials, namely, above 1300 C. and up to about l600 C.

In the preceding, I have illustrated my process in some detail with respect to butane as raw material as well as methane. There are, however, a number of other raw materials which can be treated within the same temperature range and under similar conditions. For approximately best operation from each of these, the range of expansion should be; for propane, 2.0 to 3.6, preferably 3.0; for ethane, 2.1 to 2.9, preferably 2.5; for methane, 1.6 to 2.2, preferably 1.9. For the olefines, expansions would be set slightly lower than the corresponding parafilns.

For mixtures of any of the materials herewith listed, expansion should be computed as though each component expanded alone according to the figures above given. Thus, an arithmetic average that takes into consideration the volumetric analysis of the raw material mixture, will give the favored range of expansion.

With further reference to conditions prevailing in my cracking tube 20, I assume that the temperature of the preheated feed to the crack.- ing tube is at least about 900 C. I assume a temperature rise in the cracking tube of, for example, from- 900 C. to preferably around 1350" C. or an. arithmetical average temperature of about 1125 C. For this temperature it my be I stated that the residence period for the 4-inch tube under consideration may lie between 0.12 and 0.002 second, and in many instances these limits may be further narrowed to 0.02 to 0.004 second.

As already indicated to some extent, the rate of reaction for methane is somewhat slower than for other materials. Hence, lower rates oi flow may be used, excepting when considerably high temperatures are employed. However, residence periods with respect to methane are within the limits aforementioned. It may be further mentioned that when employing methane, dilutions toward the lower limit are preferred. In general it may be said that the residence period (time interval) may be between about 0.01 to 0.004 second. My reaction is generally conducted at space velocities in excess of 100,000 and in many instances in excess of 200,000.

While I have illustrated the use of a 4-inch tube, it is to be understood that my invention is not restricted to such construction. I may employ larger or smaller tubes having thicker or thinner walls. I may also elect to use a specially adapted metal or other metal alloy in relatively thin gauge, which would be coated externally or internally or both with a vitreous enamel of high softening point. In lieu of enamel externally there might be formed an adherent oxide face. In place of enamel there might be employed the carbidizing of one or more of the elements in the metal walls.

From Fig. 1 it may be seen that the acetylene, ethylene andother products which may be produced by my process such as benzol, toluene, xylene, naphthalene are separated at various points. 'The naphthalene and the like may be taken out in the filters. I find that the residual gases leaving the unit 00 at 62 may be comprised of 50% or more hydrogen and as such, form an exceptionally good fuel for my process. Hence, as aforementioned, this fuel may be fed to burner It is therefore apparent from the preceding that my invention is suspectible of modification. Hence, I do not wish to be restricted, excepting insofar as is necessitated by the prior art and the spirit of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

I. A method for the manufacture of unsaturated hydrocarbons including acetylene from feed materials essentially comprised of nonacetylenic hydrocarbons suitable for decomposition into acetylene and olefines, which comprises preheating said feed materials to temperatures in excess of 750 C. for a period of time less than 5 seconds, sufiicient to form some acetylene in the preheated feed, but insufilcient to cause the formation of substantial quantities of carbon monoxide therein, substantially immediately subjecting the feed in its preheated condition to further heating at temperatures between 1150 0-1450" C. for a period of time less than onetenth of a second for forming substantial yields of acetylene and oleflnes, rapidly cooling the acetylene materials which have been formed, separating and recycling to the feed at least a part of said oleflnes.

2. A process for the manufacture of acetylene, which comprises obtaining hydrocarbon material essentially composed of non-acetylenic hydrocarbons suitable for decomposition into acetylene and ole-fines, diluting the hydrocarbon material with steam, subjecting the diluted material to a preheating at a temperature greater than 750 but less than about 1l00 0., for a period less than 5 seconds, sufficient to obtain a gas expansion between about 2-3 and some acetylene formation, but insumcient to cause material carbon monoxide formation, subjecting the preheated materials immediately to a further heating at a higher temperature, but less than 1600 6., and for a shorter period to obtain additional gas expansion with substantial acetylene formation, and rapidly cooling the resultant gases containing acetylene.

3. A process for the manufacture of acetylene, which comprises diluting hydrocarbon material capable of forming acetylene and olefines, with steam at a dilution ratio between about 3-18. subjecting the diluted materials to a preheating at temperatures in excess of 750 C. but less than about 1050 C. for less than 5 seconds, in a zone having an area ratio between about 25-100, to obtain some acetylene formation, immediately feeding the preheated product at a temperature within the aforementioned range to a pyrolysis treatment for a fraction of a second at a higher temperature not greater than about 1600 C. to

obtain a gas expansion of the preheated product to between about 2.5-5, and rapidly cooling the gases containing acetylene which have been formed.

4. A process for the manufacture of acetylene, which comprises diluting hydrocarbon material essentially composed of non-acetylenic hydrocarbons suitable for decomposition into acetylene and olefines, with steam at a dilution ratio between about 3-18, subjecting the diluted materials to a preheating at temperatures in excess of 750 C., but less than about 1050 C. in substantially noncatalytic metal tubes for a period of time suflicient to cause the formation of some acetylene but less than 5 seconds and insuflicient to cause the formation of more than about 5% carbon monoxide, immediately feeding the preheated product at a temperature within the aforementioned range to a pyrolysis treatment for a fraction of a second at a higher temperature greater than about 1600 C. in ceramic apparatus to obtain a further gas expansion of the preheated product to between about 2.5-5, and rapidly cooling the gases containing acetylene which have been formed.

5. A process for the manufacture of acetylene from hydrocarbon material containing volatile sulphur ingredients, which comprises diluting said hydrocarbon material with steam but only a small amount thereof so that any steam in the diluent forms a mixture with the hydrocarbon materials, having a dilution ratio less than 6, subjecting the diluted mixture to preheating sufilcient to cause the formation of some unsaturated hydrocarbon but for less than about seconds, at temperatures between about 800 C. and 1050 C., then without substantial cooling, subjecting the preheated materials for a fraction of a second to a higher temperature not greater than 1450 C. to obtain a gas expansion between about 2.5-4.2, and rapidly cooling the gases containing acetylene which have been formed.

6. A method for the manufacture of acetylene from hydrocarbon materials containing small amounts of at least one volatile sulphur ingredient, which comprises diluting the hydrocarbon with steam in a dilution ratio less than about 5, supplementing the steam diluent with another diluent more inert than steam, preheating the mixture at a temperature greater than 800 C. but less than 1000" C. for a period sufflcient to cause some gas expansion but insufiicient to cause substantial carbon monoxide formation, turther heating the mixture in its preheated condition at a higher temperature less than 1600 C. for a fraction, of a second, and rapidly cooling the acetylene-containing gases produced.

'I. A process for the manufacture of acetylene trom hydrocarbon materials, which comprises preparing ahydrocarbon material with any steam therein in a dilution ratio less than 6, subjecting the hydrocarbon materials to preheating for less than about 10 seconds at temperatures above 800 C. but less than 1100 C., immediately after the preheat injecting steam into the preheated materials, then subjecting the materials to ahigher temperature not greater than 1500" C. for a fraction of a second; and rapidly cooling the gases containing acetylene which have been formed.

8. A process for the manufacture of acetylene by procedure including the preheating of hydrocarbons in a preheater having a content of nickel which under conventional operation would promote undesirable side reactions, which comprises diluting the hydrocarbon material with steam in a dilution ratio between about 3 and 6, subjecting the mixture to preheating in said nickel-containing preheater at between about 800 C. and 1025 C. for a period suflicient to cause some oleflne formation but for less than about 5, seconds, substantially immediately subjecting the preheated mixture to heating at a higher temperature and for a shorter period but at a temperature below 1600 C. to cause the formation of acetylene, and then rapidly cooling the acetylene-containing gases.

9. A process for the manufacture of acetylene by procedure including preheating of hydrocarbons in a preheater containing a content or nickel greater than 2%, which comprises diluting the hydrocarbon material with a small amount of steam to give a dilution ratio less than 6, subjecting the mixture to preheating in said nickelcontaining preheater at between about 800 C. and 1050 C. for a period which causes some gas expansion but for less than about 5 seconds, adding further steam to the materials beyond the preheating, then subjecting the mixture to heating at a higher temperature, less than 1600 C., for a fraction of a second, in a ceramic reaction zone to cause the formation of acetylene, and rapidly cooling the acetylene-containing gases.

RUDOLPH LEON ARD HASCHE.

/ CERTIFICATE OF CORRECTION. Patent no. 2,256,555.

RUDOLPH LEONARD HASCHEQ It is hereby certified that error appears in the printed specification of the above' numbered patent requiring correction as follows: Pagelg, second colimm, line hffor the word "with" read ---from-; page 5, second column, line 65, for "splphur" read --sulphur-; page 6, second column, line 52, for "realtion" read -relation--; page 7, "first column, line 50, for "14.0" read --2.0--; and second column, line 26, for "carrynig" read --car ry ing page 8, second column, line 20, for suspectible read -susceptib1'e--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of May, A. D. 19m.

April 1, 191m.

Henry Van Arsdale (Seal) Acting Commissioner of Patents

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