US2443210A - Quenching of hot gases - Google Patents

Description

' INDIRECT HEAT EXCHANGER RTQR' WARM PRODUCTS HEAT Y TRANSFER ZONE ENCHING J. D). UPI-IAM QUENCHING OF HOT GASES Filed Dec., 2o, 1943 ACETYLSENE- PRoDuclNG ZoNe cYcLoNE/ SEPARATOR ACTIVE W /B 0 O H x @ZON wzoN D mmumzq. 5G.: l. aumzw 51 3 0 T R T p v m Mw f Mm Rm 4 ZON HB m www. www W ZOVCQN mjom C I Mm m U M m O 5 /o m wm M@ WM O O OR A n m T f W\ /4 m S R T O T w D M D l T nAe 3 O w M 6 M NM w. w F w WM 1 3 2 S SC A .4 6 R "IW-E .g 1V llvl ASN T n T mZON ZOrZmwOmQ mo 9 EMO m o Tmsms Hmm. m h W A B/ LNL \\UN M l @www mn.. 0 C 7 Zorrmzwwmm .el .al

june l5, 1948.,

Patented June l5, 1948 QUENCHING OF HOT GASES John D. Upham, Bartlesville, Okla., asslgnor to Phillips Petroleum Company, a corporation of Delaware Application December 20, 1943, Serial No. 514,989

12 Claims. l

This invention relates to the rapid and emcient transfer of heat between fluids and solids. In a preferred modification it relates to the quenching of hot conversion gases containing highly reactive materials such as acetylene or butadiene. A further embodiment relates to the recovery of heat from such hot gases and reutilization of such recovered heat in the conversion process.

The production of highly reactive unsaturated organic materials has become very important industrially, for example as evidenced by the increased demand for the hydrocarbons acetylene and butadiene, The highly reactive nature of these materials, which is the property which gives them their value. at the same time presents serious obstacles to their successful production. For example, most practical methods of making acetylene or butadiene from hydrocarbons, which are by far the cheapest and most abundant possible raw materials, involves a high-temperature catalytic einen-catalytic pyrolysis of the hydrocarbon feed stocks. The optimum time for these feed stocks to be held at the elevated conversion temperatures is of the order of from a few seconds down to a few hundredths of a second or even less than one hundredth of a second at the highest temperatures. Lengthened reaction periods allow secondary reactions, and decomposition or other reactions of the product, to become predominant, resulting in a decreased ultimate yield due to destruction of raw material and/or product.

Acetylene, for example, may be produced by the cracking of almost any hydrocarbon material at temperatures above about 1250 F., and fairly high yields of commercial interest may be obtained when working above about 1800 F. on up to about 3000 F. or even somewhat higher. At such elevated temperatures, however, the cracking process continues with the production of carbon and hydrogen, and. the acetylene also forms polymerization and other condensation products readily. Accordingly, the residence time of the hydrocarbon reaction mixture must be quite limited, and the cracked hydrocarbons must, upon completion of the desired conversion, be immediately quenched to a temperature at least as low as about 900 to 1000 F., and preferably lower, such as down to about 550 F. This fact is well known to the art. and many methods of carrying out the quenching have been proposed.

These known methods involve quenching with liquids, for example, water, alkaline solutions, charging oil, etc. Certain defects are inherent in the methods heretofore proposed or used, which defects include loss of small but valuable amounts of aromatic oils, carbon black, and other components of the mixture, and loss of great amounts of heat which are absorbed by the quenching medium and either completely wasted or only very incompletely and ineilciently utilized. If the liquid to be cracked is used as quenching medium, it is apt to be contaminated by absorption therein of material from the cracked gases. Passage of the hot cracked gases over Wateror air-cooled heat transfer surfaces, such as metal plates, is of course inem-cient in bringing temperatures down rapidly.

Somewhat the same considerations apply in the case of diolefins such as butadiene, isoprene, -pipery1ene, etc., formed by high-temperature conversions, which may be non-catalytic or catalytic. Polymerization and decomposition reactions normally occur at a rapid rate in the diolefln-containing eilluents of such conversions. For example, in a butene dehydrogenation, vapors leaving the dehydrogenation catalyst at temperatures of about 1100 to 1300 F. may contain only traces of polymer, but rather high percentages of highboiling polymers are found in the dehydrogenated l vapors after normal cooling to temperatures in the range of say to 300 F. The polymerization reactions involved may be illustrated. using general formulas, as follows:

MonomerdimerT-*higher polymers At high temperatures of the order of 1000 F. equilibrium is established in extremely short times, but the concentrations of dimer and higher polymer at equilibrium are very small. At low temperatures of the order of 200 to 300 F., the equilibrium is established so slowly that little dimer is normally formed even though equilibrium concentrations allow the formation of high percentages. At intermediate temperatures, however, both the time required to establish equilibrium and the equilibrium concentrations are v favorable to dimer and higher polymer .formation.

For example, a temperatures around 1200 F. the quantity of dimer formed at equilibrium from butenes is less than 1 per cent, but this quantity increases to about 5 per cent at temperatures near 700 F. Butadiene is even more readily polymerized, and at temperatures of 700 to 1000 F. a very considerable quantity of the diolen may exist in the dimeric form at equilibrium. copolymers formed between butenes and butadiene are also more readily formed than butene "endemo polymers, and may account for a further amount of polymer formation. Thus it has been found that serious losses of butadiene may occur subsequent to the catalytic dehydrogenation step while the eiuent vapors are being cooled if sufy ilcient time elapses for equilibrium concentrations of polymers to be attained in the temperature range of rapid polymerization.

The polymerization reaction velocity is enormously greater at temperatures Just below the dehydrogenation range than it is at low temperatures such as those finally attained by the cooling system. Consequently, the formation of large amounts of polymer in the cold eiiluents does not occur in the absence oi' catalyst, even over very long periods of time. On the other hand, in the range from dehydrogenation temperatures down to about 600 to 800 F. polymerization reaction rates are still extremely high so that equilibrium concentrations are approached in a few seconds or less. The large quantities of polymer formed are therefore accounted for by equilibrium concentrations of polymers being formed as the gases are brought down through this active temperature range in conventional cooling equipment, wherein the cooling period is relatively long. Below about 600 to 700" F. the reaction velocity of polymerization becomes too small to cause measurable losses, even when the cooling period is prolonged. It has been noted that when carrying out the dehydrogenation of butene quantities of polymer varying from about two to about ten per cent of the butene charge are often formed while conversion to butadiene is only of the order of about fourteen to twenty-four per cent. Thus. the loss of dioleiln due to polymerization which may largely occur after the eilluent vapors leave the catalyst may be seen to be very serious.

In quenching hot butadiene-containing streams in conventional manner, much the same defects or disadvantages are encountered as those recited above with respect to conventional quenching of acetylene-containing streams. Inasmuch as most processes for converting hydrocarbons to dioleiins or acetylenes at elevated temperatures involve relatively low per-pass conversions to the desired products, normally ranging from say l to 40 or 45 per cent, unconverted components are separated from the conversion eilluents and recycled for further conversion. This entails a heating of 100 parts of hydrocarbon to conversion temperature to produce, for example, parts of product. The 30 parts of product, together with 70 parts of unconverted material, disregarding losses by side reaction and asby-products, are quenched.

-and the '70 parts must be re-heated. In other words, in this typical instance, for each 30 parts of product formed, about\ 70 parts of material are heated to a high temperature and then cooled without having undergone useful conversion. The wastage of heat involved, if adequate means are not provided for its recovery and reuse, is apparent. These various problems are encountered not only in the non-catalytic formation of acetylene by pyrolysis and the catalytic formation of butadiene by dehydrogenation. but also to a greater or lesser extent in any high-temperature catalytic or non-catalytic process wherein highly reactive materials, such as vinyl acetylene, methylacetylene, isoprene, piperylene, acrylonitrile. styrene, ethylene oxide, etc.. are formed to an appreciable extent. f-

It is an object of this invention to quench hot gases containing highly reactive materiale in all eifective manner. Another object is to accomplish such quenching without encountering certain defects of conventional methods. A further object is to quench hot dioleiinand/,or acetylenecontaining conversion mixtures with adequate rapidity to avoid undesired side reactions and/or decomposition or polymerization of the products. and further to recover a substantial proportion of the heat content of -such mixtures for re-use in the conversion. Another object is to provide a complete cyclic heat transfer process wherein cold or heat is imparted to a stream by a' direct transfer step, the stream is then utilized in desired manner, and at least a portion of the cold or heat imparted thereto is then recovered by a direct heat transfer step for reuse. Other objects and advantages of the present invention will be obvious, to vone skilled in the art, from the accompanying disclosure and description.

Briei'ly stated, in preferred embodiment my invention contemplates eiecting a direct admixture of relatively cool mobile solid heat retentive or absorptive material with a hot hydrocarbon conversion emuent which itis desired to quench, said heat retentive material being used in such quantitiesy and at Such a temperature. and having such a specific heat and heat conductivity, as to eiect an adequately rapid or substantially instantaneous quenching of the hot effluents to a temperature level sufficiently low as to avoid undesired reactions. This direct admixture is accomplished by passing separate streams of hot eiiluents vand of relatively cool mobile heat retentive or absorptive materialintoa common mixing zone. By a mobile solid heat retentive material I mean a solid material. having desirable thermal properties as described below, and in particulate form so that it may be readily moved as a ilowing stream through the system. The individual particles of the heat retentive material may, under various circumstances, range from a few microns in diameter up to fairly large particles of say about one inch or even somewhat more in diameter. The choice of particle size for any particular application will be gove ed by factors to be discussed more fully herein ter.

After a thermal equilibrium has been substantially established between the heat retaining material and the eilluent conversion stream in the mixing zone referred to. which is accomplished quite eiiiciently `due to the direct transfer of heat between iluid and solid, the quenched eiiiuent stream is separated from the heat absorbent and passed to further treatment as required.

` The so-separated heat absorbent, havingtaken up a substantial amount of the sensible heat of the hot hydrocarbon eiliuents 'and being thus heated, is next passed in a stream into a second mixing zone wherein it is contacted with'cdol iluid hydrocarbon feed which is to be converted. In this mixing or heat-transfer zone the relatively hot heat retentive material is cooled by the feed stream, which concomitantly becomes heated by contact with the heat absorbent. It will be seen that a substantial amount of the heat absorbed from the converison eilluents is thus directly and accordingly emciently transferred to the incoming feed and conserved for re-use in the conversion. After approaching thermal equilibrium as closely as desired in the second mixing zone, the hydrocarbon feed stream is .separated from the stream of heat absorbent and passed to the conversion step, ordinarily iirst undergoing additional heating to supply heat for the conversion which is usually endothermic and to make ammo absorptive material which may be utilized. De-

sirable thermal qualities in such a material involve a high specific heat, high density, and high 4heat conductivity. It will be appreciated that the term high is a relative one, and that accordingly a wide range of materials may be useful in carrying out the invention, the choice of a particular heat absorbent being dependent on the conditions under which it is to be applied. It will further be understood that a given heat absorbent may be entirely satisfactory in one situ--` ation but not so suitable or even entirely unsuitable in a different situation. The material must of course have a melting point appreciably above the lmaximum temperature which is likely to be encountered, and must also be able to withstand suchmaximum temperatures without undergoing other undesirable changes. Ordinarily the heat retentive material is substantially inert under the conditions of use with respect to the fluids to be contacted and to the apparatus, and is preferably of a non-adsorptive nature. However, in accordance with certain modifications of the invention, a material having a catalytic or other effect upon one or more of the fluids contacted is used. With these general limitationsin mind, a listing may be made of some examples of materials suitable under various conditions for use in carrying out the invention. This listing is, of course, not intended to be all-inclusive, and many other suitable materials will be suggested to one skilled in the art by the disclosures offered herein.

The metals may be cited as one class of materials. With respect to thermal properties, the metals 4are more desirable than any other class of solids. However, certain of the metals are highly reactive, and hence may not be suitable for use in the presence of oxidizing or other active gases, such as those containing free halogens, acids, etc. Furthermore, the melting points of the metals are of course to be taken into consideration in making a choice for a specific quenching or other heat transfer step. The metals, and in fact all solids, vary between one another in heat conductivity much morethan in specific heat or density. For example, most metals operative in this invention have specific heats, at elevated temperatures of the order of 800 F., of between about 0.1 and 0.3 B. t. u. per pound per degree Fahrenheit. and few solids of any kind have specific heats much4 above about 0.4 under similar conditions. 'I'he densities of most metals are roughly in the range of about 400 pounds per cubic foot. although thelighter metals Amay be less than 200 pounds per cubic foot, and

most non-metallic refractory solids which may be used in the present process have densities between about 100 and 200 pounds per cubic foot. In contrast, the heat conductivities of suitable metals may vary from about 200 B. t. u./hr./sq. ft./'F./inch in one case up to over 2000 in another case, and non-metallic solids which may be given consideration for use in carrying out my invention may have heat conductivities as low as 1. It is accordingly apparent that inselecting a group of solids having properties other than thermal properties suitable for a given lapplication, most of the solids in the group will be similar with respect to density and specific heat, while they may be quite dissimilar with respect to heat conductivity.' From such a group, then, withl due consideration being given to cost and other such factors, a solid having a high heat conductivity would ordinarily be selected for actual use. and specific heat and/or density would play a part in the final selection only in deciding between two or more solids of similar high heat conductivity.

Returning now to the metals, the following may be mentioned merely as examples having relatively high melting point, and are listed approximately in decreasing order of heat conductivity, that is from the highest to the lowest: copper, aluminum, brass, nickel, iron, mild steel, chromium alloys, etc. The thermal conductivity of the highest in this list, copper, is more thanv ten times that of the lowest in the list, chromium alloys, the former having a conductivity at -1000 F. of about 2400 B. t. u./hr./sq. ft./F./in., and the latter having a conductivity of about 200. The above list of course is not exhaustive but merely suggestive, to one skilled in the art, of

the wide variety of materials available and their range of properties. Choice of a metal for a specific quenching or other heat transfer step or cycle carried out in accordance with the teachings of this disclosure is made by taking into consideration first the melting point as compared with maximum temperatures prevailing in the system, then the chemical suitability. After some metals are thus eliminated, consideration is given to the availability and cost of the remaining suitable metals in desired particle size and/or shape, then the heat conductivity and finally, if more than one metal still appears suitable, the density and specific heat are taken among the determining factors.

Considering now the non-metallic solids, it is' immediately apparent that a lower order of heat at high temperatures, a non-metallic solid is frequently more deisrable than a metal. Artificial graphite and silicon carbide (Carborundum) are outstanding in that their heat conductivities are far above those of any other non-metallic solid investigated. Graphite ranks with most of the metals, while silicon carbide is below the metals but still far above other non-metals. Due to its inertness. heat stability, and mechanical strength, silicon carbide is usually preferred over graphite in the practice of my invention. The heat conductivity of silicon carbide varies considerably with temperature, but generally speaking is within the range of about 100 (in the units used above), varying from '75 at 2500 F. to 125 at 1100 F. The reasons for my preference for silicon carbide thus become apparent when its thermal, mechanical, and chemical characteristics are-considered.

Other non-metallic solids available for use in various modifications of the invention include the following examples listed in approximate decreasing orderof heat conductivity (at elevated temperatures of 1500 to 2000 FJ, which ranges from about 25 to 30 on down to about 1 to 2: petroleum coke, fused alumina, magncslta-V quartz, other formsof dense silica, ilreclay, porcelain, rocks of various kinds, diatomaceous earth (fired), etc.

The methods of handling any of the foregoing -or other heat absorptive materials depends, among ing from a fine powder up to balls one inch in diameter are described in the examples shown in the drawings, and will be considered in detail below. Choice of particle size will be based primarily on the rapidity of vheat transfer required, with secondary consideration being given to the thermal properties of solids available, particularly ii' the number of suitable solids is somewhat limited. For a very rapid quenching, such as is required for example in the case of an acetylene-containing stream obtained by pyrolysis of an oil in the electric arc, small particle size is most advantageous and indeed almost essential. Thus, in a preferred embodiment described below a moving stream of finely comminuted solid heat absorbent is injected into the hot converted stream whereby the hydrocarbons are almost immediately reduced to the desired low temperature. As another example. wherein quenching is not of such importance or of no importance, but wherein a most complete utilization of heat or cold is desired, relatively large particles of heat absorbent are caused to pass counter-current to a hot or cold fluid, sumcient residence time being allowed to obtain substantially complete thermal equilibrium at the various points within the heat transfer zone. In any case. the particle size, heat conductivity, and heat capacity of the solid material are correlated to give the desired rate of heat transfer. Under the term mobile solid heat absorbent may also be included chains, continuous ribbons of metal, continuous sheets of metal wool, etc.. which by suitable mechanical means may be caused to flow as rapidly as desired as a stream through the required apparatus in direct contact with fluids. However, somewhat complicated driving and guiding means are generally required; and due particularly to the ease and ilexibility in handling, as well as generally superior heat transfer properties, a large number of separate, individual particles, as described above, is ordinarily preferred.

It is felt that a more complete understanding of the principles of the invention may now be obtained, based on the foregoing disclosures, by examining the operation of certain processes wherein said principles are relied upon in attaining the objects of the invention. Reference is accordingly made to the accompanying drawings, 'which portray in a schematic manner principal elements of equipment in which the invention may be practiced. It will be appreciated that the representations in the drawings are diagrammatic in nature, and that numerous additional pieces of equipment, such as heaters, pumps. control instruments, valves, insulation, ow rate regulators, product separators, steam lines, etc. will be used in any given operation. However, the supplying of such items is well within the skill of the art, and further mention need not -be made of them in view of the detailed and adequate disclosure presented herein of various preferred modes of carrying the invention into practice.

Figure 1 shows diagrammatically apparatus used in producing acetylene by non-catalytic pyrolysis of hydrocarbons, wherein quenching and heat recovery are effected in accordance with the invention.

Figure 2 shows diagrammatically apparatus used in producing butadiene by the dehydrogenation of butene in the presence of a powdered dehydrogenation catalyst, wherein quenching and heat recovery are effected in accordance with the invention.

Figure 3 shows diagrammatically apparatus U. s. Patent 2,387,731.

cold from the product is effected in a complete cycle in accordance with the invention.

In Figure 1, a cracking zone i0, designed in accordance with principles well known in the art, is provided for producing acetylene by Dyrolysis of a hydrocarbon feed stock which enters feed may range from ubstantially pure methane up to heavy reduced crude oil or other heavy liquid hydrocarbons, and may comprise one or a plurality of individual hydrocarbons., It will Ibe appreciated that the exact methods of operating will vary in accordance with the nature of the feed stock, as will the temperature and residence time in the conversion zone. Frequently steam, hydrogen, and/or other diluents will be used in conjunction with the hydrocarbon material. Partial oxidation with oxygen-containing gases may also be used in order to attain the required high cracking temperatures. In addition to acetylene (C2H2), other higher acetylenic hydrocarbons will be produced in smaller quantities, as will monooleiins, dioleilns. other unsaturates, aromatic oils, relatively large quantities of hydrogen, etc. Depending upon pyrolysis conditions, appreciable amounts of carbon black may be formed. The cracking zone I0 may comprise an electric arc, but preferably comprises a regenerative-type furnace containing refractory brickthe system throughane Il. The hydrocarbon work or the like which is alternately blasted with l hot combustion gases or flame and then used for passage of the cracking stock therethrough wherein the desired cracking occurs due to the high temperature of the refractory material. The construction and operation of one such furnace is described by Hasche et al. in U. S. Patent 2,319,679. Reference may be hadto the literature for a complete discussion of charging stocks, diluents, partial combustion, arcs, furnaces, temperatures, reaction times, products, product separation, etc., and these aspects will not be further described here. Ellis, The Chemistry of Petroleum Derivatives, volumes I and II and references cited therein,; numerous patents to Wul such as 2,037,056, etc.; Metzger, 2,179,379; are

cited as examples of the literature dealing with acetylene production and related subjects.

Although the extreme temperature used in producing acetylene are not ordinarily attained, the embodiment of the invention illustrated in Figure I may also be readily applied to the catalytic or non-catalytic production of butadiene. Higher temperatures are encountered when gases or oils are non-catalytically cracked, frequently in the presence of superheated steam or oxygen. By Way of examples may be mentioned the processes disclosed in copending application by Allen and Wolk, Serial No. 496,090 now U. S. Patent 2,377,847, and by Alleny Serial N o. 493,671 now Frolich et al. disclose a high-temperature, low contact time pyrolysis of butene-2 to produce butadiene in U. S. Patent 2,322,122. Other processes are knownv to the art, suchas those mentioned by Ellis in The Chemistry of Petroleum Derivatives.

In the embodiment shown in Figure 1 as applied to acetylene production, a finely divided heat absorbent is used for quenching and heat recovery. Due to the extremely high temperatures involved, which may in some cases range as high as 3000 F., I prefer to use silicon carbide particles as heat absorbent. inasmuch as avery rapid quenching is required, particles which will pass through about a 100 mesh screen, or at least through a 60 mesh screen, are used. lSilicon carbide or Carborundum powder of 200-300 mesh is advantageously employed. The small particle size, coupled with the high heat conductivity of silicon carbide, makes possible the highly satisfactory results which are obtained. The silicon carbide is substantially non-catalytic and hence desirable for this reason also.

Reactants and reaction products pass through the system in the following order: enter through line Ii,pass through indirect heat exchanger I2.

' line I4. heat transfer zone I6, line I separator 2l, line 22, heater 24 if required or by-pass line 25, 'line 28, cracking zone l0, line 28, quenching and heat transfer zone 20, line 22, separator 34, line 28, indirect heat exchanger I2, and out via line 28 to conventional separation and recovery treatments. Into the extremely hotr conversion eiiluents stream passing through line 28 is continuously injected a stream of relatively cool heat absorbentpowder from line 40. The powder, becoming immediately suspended in the gases, effects a Very rapid quenching to a temperature, such as 800? F., at which undesired reactions are minimized or stopped entirely. The direct heat transfer involved between gas and solid is highly eillcient in obtaining the desired results. The mixture of gas and solids is allowed to remain in heat transfer zone 30 for a sufficient length of time for substantial attainment of thermal equilibrium, or at least until the gas is cooled to the desired low temperature. The time required for this is quite short, such as one or two tenths (0.1-0.2) of a secondor less, and the size of zone Il is determined by the rate of flow through the system; the quenching zone 3o may actually consist merely of a suiilcient length of conduit, rather than a separate chamber as shown. The streams 2l and 40 may be injected separately or together into the quenching zone.

In case a' hot stream from a butadiene-producing conversion is being quenched, the hot butadiene-containing gases `are preferably quenched to a temperature below about 700 F. within a period of time less than about one second, and preferably less than about 0.2 second.

The mixture of vapors and solid particles is next passed into separator 34, which may be a filter, electrical preclpitator, or other suitable means, but which preferably comprises a cyclone separator. From this separator the quenched gases, now substantially free from the powdered heat absorbent, may be passed through indirect heat exchanger l2 for imparting some of its residual sensible heat to the incoming feed, andthen on to suitable treatment known to the art for recovering the desired products and recycle stock, if any. The gases leaving separator 34 may in some cases require additional treatment by means not shown for removal and recovery therefrom of traces of powdered heat retainer. Under severe conditionsf'of :pyrolysis in zone I0. appreciable amounts of carbon may be formed. This carbon may at least partially pass through separator 3d and be recovered from the quenched gases by known means, whereas if a liquid quenching medium were used the carbon would be retained in admixture with the liquid. Any carbon separating withthe heat absorbent powder in separator 34 is readily recovered therefrom by virtue of density differences.

The powdered silicon carbide or the like recovered in separator 34 is now at a considerably 4 10 more elevated temperature than prior to ltsuse in quenching zone 2l, and has absorbed a substantial proportion of the sensible heat of the conversion mixture. This recovered heat is,y re.used in the process .by passing the powder through a complete cycle including another heat transfer zone il. The hot powder is passed vialine I2 into admixture with the relatively cool incoming feed in line I4, and the mixture resides in heat transfer zone I6 for a sufficient time to reach or at least' approach thermal equilibrium. By this means the recovered heat is re-ixnparted to the feed, and

the hot absorbent is concomitantly cooled by the cool feedand thus reconditioned for use as a quenching medium. Eiiluents from zone I6 pass via line I8 into separator 20, which is preferably a cyclone separator similar to unit 34, and the thus-preheated feed exits through line 2 2 and may be passed directly via lines 25 and 28 to the cracking zone, or may be given additional preheat in heater 24, depending upon the characteristics of the cracking system. Cooled powder from separator 20 is passed via, line 40 for reuse as a quenching' and heat recovering medium in zone 30 as described. The powder may be addi-y tionally cooled by means (not shown) inserted in line 4B if desired.

The powdered heat absorbent may be conveyed through its cycle by any means known to the art. This may include mechanical means such as screw conveyors, etc., supplied within lines 40 and 42. Preferably gravity is relied on to carry the stream of powder in one or both of these lines. The gas-lift principle may be utilized if desired in moving the powder in known manner. Due to the abrasive .character of silicon carbide, suitable protection is provided for equipment carrying the powdered solid. Preferably this comprises a 1ining of silicon carbide. Itwill be understood that in view of the extreme temperatures involved, the equipmentcomprising cracking zone Hl, as well as line 28, and zone 30 and line 26 if required will bon present in the eilluents is readily separated from the heat carrier powder. Aromatic and/or unconverted cycle oils which it may be desired to recover are simply separated from the carborundum. Due to its non-adsorptive nature, very little of this type of material is Picked up. A periodic washing of the powder with suitable solvent may be'used to recover such material from admixture therewith in certain cases. Also, in

the event a carbonaceous coating is developed on the silicon carbide powder, an occasional oxidation will serve to remove same.

While silicon carbide has been described as the preferred material to use as a mobile solid heat carrier in the embodiment of the invention shown in Figure 1,' other refractory material, such as alumina, iireclay, silica, fine quartz sand, etc., may be used with suitable modifications in the quantities used, and with due consideration being given to the temperature involved.

Turning now to Figure 2, for a consideration of another embodiment ofmy invention, the now of 11 f materials for the catalytic dehydrogenation of butenes to butadiene is shown in diagrammatic form. The conditions required and the numerous catalysts which may he utilized, the use of diluents and various other modifications, will not be discussed in detail, inasmuch as these factors are well known and it is clearly within the skill of the art at this time to practice butene dehydrogenation in the presence of a powdered catalyst to produce butadiene. To amplify the details further would only encumber the present disclosure without furthering an understanding of the invention. In this embodiment, the mobile heat absorbent material used for quenching and heat recovery is the catalyst itself. The catalyst is obviously capable of withstanding the temperatures to be encountered. Suiilcient is used to provide a heat capacity great enough to quench the dehydrogenation effluents to the desired temperature. Preferably substantially spent catalyst, that is, catalyst which because of carbonaceous deposits is incapable of furthering the dehydrogenation reaction emciently, is utilized. The advantage gained is that the quenching material may then be considered to be a substantially inert or non-catalytic, and yet no extraneous material is brought into the system. Carry-over of catalyst powder into the heat transfer system, or of heat absorbent powder into the catalytic system, accordingly need not be feared, and preferably the two systems named are inter-connected, and` in fact are overlapping in the embodiment shown in Figure 2.

As catalyst and heat absorbent may be mentioned merely by way of example composites of chromium oxide with a major proportion of alumina, preferably treated with minor amounts of alkali metal hydroxide or other alkaline material, and containing limited amounts of barium or strontium oxide. Such a catalyst is preferably used in conjunction with steam as a diluent for the olefinic dehydrogenation feed. Numerous other dehydrogenation catalysts might be mentioned without adding to the knowledge of the art, for any suitable dehydrogenation catalyst may be used with suitable modification. A mesh size of 200-300 is satisfactory, although other sizes may also be used. Any known manner of handling the mobile catalyst may be used. Dehydrogenation temperatures of 1100 to 1300 F. are suitable for the production of butadiene, although dehydrogenation temperatures outside this range are also operative. For the dehydrogenation of pentenes to produce pentadienes, for example, somewhat similar temperatures are suitable. The feed stocks need not necessarily be entirely oleflnic, for normal butane may be dehydrogenated in a single stage to butadiene, preferably with recycle of butenes. Moderate superi atmospheric pressures, such as 50 to 100 pounds per square inch absolute, are ordinarily used, although somewhat higher or lower pressures, even sub-atmospheric pressures, are sometimes used.

In Figure 2, normal butene feed, which may be 1butene, 2-butenes, or mixtures thereof, together wih propylene, hydrogen, steam, carbon dioxide, or other diluents and/or hydrogen acceptors as desired, is passed via line 6I, through indirect heat exchanger 62, through line 63,

heater 64, and line 65 to dehydrogenation zone 66. Powdered catalyst from conduit 61 is introduced, as by injection, into lthegases in line 65 just prior to entrance into zone 66, or directly into zone 86. 'I'he suspension of catalyst in reactants passes through zone 66, wherein the de sired dehydrogenation takes place.

f .This suspension then leaves zone 66 via line il, into which is introduced from line 69 a relatively large quantity of additional powdered catalyst which is initially at a temperature well below that of the dehydrogenation eliluents. The resulting mixture resides in heat transfer zone 1lv until thermal equilibrium is substantially vattainednJ-The injection of cool catalyst in this manner very rapidly quenches the reaction mixture to a temperature below that at which undesired reaction occurs. The mixture passes from zone 10 via line 1| into separator 12, preferably a cyclone separator. Gases leave separator 12' substantially free from catalyst, via line 13,heat exchanger 62 and line 14. These gases are then subjected to conventional treatment for recovery of components including butadiene, hydrogen,

`and recycle stock. If desired, methods now known to the fluid catalyst" art for effecting complete separation of dehydrogenation catalyst from reaction zone eilluents may supplement the separation effected in separator 12. Such meth ods include partial condensation of the gases, electrical precipitation, scrubbing with liquids, etc.

Catalyst leaves separator 12 via line15 and passes partly into line 16 and partly into line 11. From line 11, catalyst passes through cooling vmeans 18, and thence into line 68 for re-use as quenching medium as described. Catalyst from` line 16 passes to line 61 either through regenera- 'i tion zone 19 or through by-pass line 80, or both.l\ From line 61 it is again used in the reaction zonei In regenerator zone 19, carbonaceous matter is burned off, as by suspension of the catalyst in hot oxygen-containing gases, in known manner. If

the heat thus generated is insullicient to bring the temperature of the catalyst up to the desired value near the dehydrogenation temperature,

additional heating of the recycled catalyst may be accomplished by means not shown, or the preheat of the gaseous feed to the dehydrogenation may be suiiicient to give the desired temperature in the reaction zone.

It will be seen that an effective quenching is readily attained, without the necessity of introducing any extraneous substance into the reaction zone eiiluents. The catalyst is continuously flowing in a closed circuit, including an internal quenching circuit. The catalyst for quenching may be obtained from regenerated catalyst, rather than as shown, but this is generally not so desirable, for fresh catalyst would at first, at least, encourage further reaction. while spent catalyst is relatively inactive. An advantageous operation, not shown for the sake of simplicity in the drawing, is to efi'ect cooling of the quench catalyst stream in unit 16 by indirect, or preferably direct,- heat exchange with cold incoming reactants in line 6I, thus giving eicient heat recovery and utilization. This and other modifications, as well as the use of auxiliary equipment as required, will be obvious to one skilled in the art in view of the detailed disclosureof principles and specific methods herein.. f 1

In case it is desirable to avoid cooling the main vone pass through the reactor, so that most of the catalyst is recycled without regeneration.` In

13 l such an operation, the total elunts from the dehydrogenation zone may first have at least the bulk, and preferably substantially all, of the catalyst separated therefrom and recycled; The gaseous conversion products still hot and just separated from the catalyst, are then quenched by suspension therein of cool, deactivated catalyst. The deactivated catalyst thus used for quenching is separated from the quenched gases, and is preferably maintained in a circuit of its own substantially separate from the hot catalyst circuit. Small amounts of catalyst may be carried into the quenching circuit, and corresponding amounts may be withdrawn therefrom, regenerated and returned to the active catalyst cycle.

By suitable-modification of equipment, the methods just described for (powdered catalysts may be extended to moving beds of catalyst of larger particle size, such as from 4 to 60 mesh, as exemplified by the so-called TCC process. In such an instance, a larger particle size of heat absorbent would necessitate a great quantity thereof over the amount of powder required in y order to obtain a given rapidity of quenching. Longer residence times in zone would also be utilized.

The apparatus shown diagrammatically in Figure 3 may be used for carrying out a low-temperature catalytic olefin polymerization process, whereby an efficient conservation of refrigeration is obtained. A modification of my invention is thus shown which, although utilizing certain principles common to all modifications, never the less differs substantially in some respects from the modifications of Figures 1 and 2. In this instance it is not heat, but cold, which it is desired to conserve. It is realized that strictly speaking, according to the usually accepted scientific terminology, cold is not transferred from a rst facciamol point to a second point but rather heat is transy ferred from the second point to the first point.

However, when refrigeration is involved and temv peratures below normal prevail in a system, it is convenient to refer to the imparting and transferring of cold or refrigeration, since it is the refrigeration which is expensive and which accordingly it is desired to conserve. With this explanation it is believed that one skilled in the art will readily understand what is meant when such terminology is used. In the process illustrated by Figure 3, a quenching step is not required, but a most complete transfer of heat (or cold) within a continuous cycle is desired.

A polymerization zone or system, represented schematically in the drawing by the rectangle |00, is provided,` which may involve any of the features of processes of this kind which are known to the art. The desired polymerization of olefins is carried out in this system at sub-atmospheric temperatures which may range from say 40 F. on down to say 160 F. or even lower, depending on the feed stock, catalyst, and product desired. It is well known that a great variety of polymers may be prepared by the catalytic polymerization or copolymerization of one or more olefins or olefinic materials such as isobutylene,

normal butenes, ethylene, butadiene, vinyl chloride, styrene, etc. The polymerization is frequently carried out at depressed temperatures in the presence of relatively large volumes of solvent. using a Friedel-Crafts type metal or metalloid halide catalystv such as boron triiiuoride, aluminum chloride, aluminum bromide, tin tetrahalides, zirconium tetrachloride, etc. Promotors 1'4 such as thel lower alkyl halides, hydrogen halides, certain ketones, etc., are sometimes used. Generally speaking, the lower the temperature of reaction the higher the average molecular weight of the polymer, other factors being equal. Soluble and/or insoluble polymers may be formed, depending upon conditions. Ellis, Chemistry of ,Petroleum Derivatives, and other"patent and non-patent literature may be referred to for additional details. The method to be` described is particularly applicable to processes which produce soluble polymers, although with suitable modification it may be applied to insoluble polymers, such as butyl rubber, which is a copolymer of isobutylene with small amounts of a diolefin.

By way of example may be described the-polymerization of a hydrocarbon mixture containing a substantial proportion of butenes, preferablyisobutylene although normal butenes may also be present. Ordinarily a C4 fraction is used` which contains substantial amounts of butanes. which serve as diluent and solvent for the high molecular weight polymers formed. If such butanes are not available in sufficient quantity admixed with the butenes, they may be supplied, or pentane or other suitable saturated hydrocarbon solvent may be used. The butenes and accompanying hydrocarbon material, preferably in liquid phase, enter via line |0| from any suitable source, and flow through heat transfer zone |02 countercurrently to a downwardly flowing mass of cold solid heat retentive material, such as for example metal shot, chains, metal wool, metal turnings, rocks, quartz, clay, etc. Aluminum spheres of about one inch diameter are preferred, due to the high heat conductivity of aluminum,

itsinertness to the reactants, its cheapness, and y the ease of handling and fiowing such spheres. The stream of heat carrier enters the top of zone |02 at approximately reaction temperature, which may for example be about 25 F., and in flowing countercurrent to the incoming fluid reactants imparts cold thereto and thus cools the same by very eflicient direct contact. The thus precooled reactants leave the top of heat transfer zone |02 via line |03 and pass through refrigeration means |04 wherein a further lowering of temperature to or somewhat below reaction temperature is accomplished. Means |04 furnishes sulcient regrigeration to overcome the heat liberated by the exothermic polymerization reaction and also the heat entering the system from the surroundings, largely due to lack of perfect insulation.

The cold reactants next pass via line |05 into reaction zone |00, wherein they are subjected to the action of a poiymerizing catalyst such as boron fluoride or a solution of aluminum chloride in methyl chloride. Substantially complete polymerization of the butenes occurs to form polymers of a molecular weight suitable for use as lubricating oils, additives to oils, etc. A part of the refrigeration may be supplied directly to the reaction zone by means other than super-cooling of feed if desired. It is preferred to carry out the reaction as nearly isothermally as possible, for close temperature control is essential for good product control. For example, the product formed at 25 F. may have an average molecular weight several times that of the product formed at +25 F. After a. suitable residence time. the cold products of reaction, comprising a solution of polymers in liquid low-boiling hydrocarbons, leaves the like, to the top of zone |01.

l y the zone via .line Illand enters the bottom of heat exchange zone |01. In this zone a substantial proportion of theE cold previously imparted to the feed as in zone |02 is recovered for reuse.

The ,stream of mobile heat absorbent such as the aluminum spheres referred to above leaves the first-mentioned heat exchange zone |02 at a temperature well above reaction temperature. This stream is transported via conduit |00, which may have associated therewith means (not shown) such as screw conveyor, bucket lift, or By flowing downward in zone |01 countercurrent to the cold reaction effluents, the heat absorbent becomes cooled, while the products are warmed to somewhere near room temperature, the flnaltemperature of the products which exit vla line |00 being dependent on the rate of flow of absorbent and the rate of flow of hydrocarbons through the system. Effluent products from which the cold has been recovered are passed to conventional means for recovering and purifying desired polymers, solvent, etc. The stream of cooled aluminum spheres passes from zone |01 into zone |02 through a means H0 which may be a mechanical closure such as a revolving lock more or less fluid-tight or other suitable means. A certain amount of leakage of liquid through unit ||0 in either direction is allowable since eiliuents leaking\through will merely be recycled to the reaction zone, while incoming liquid leaking through will simply by-pass the reaction zone, and be treated along with the effluents in conventional manner.

The countercurrent flow just described is the most efficient for recovering the cold or utilizing the refrigeration, inasmuch as the mobile heat absorbent leaves zone |01 at approximately the temperature of the reaction eilluents, while it leaves zone |02 at approximately the temperature of the incoming feed, having given up substantially all of its cold thereto. Looked at from another viewpoint, the warm incoming feed passes in zone |02 progressively into contact with colder and colder heat retainer, being thereby cooled to a final low temperature; the cold liquid eilluent from reaction zone |00 passes in zone |01 progressively into contact with warmer and warmer heat retainer, being finally brought to a relatively warm temperature. The method of operating just described with reference to Figure 3, as well as other embodiments of my invention, are highly advantageous in that most efllcient heat transfer is obtained by the direct intermingling of fluids and mobile solids.

The heat transfer method illustrated in Figure 3 may, by suitable modification, be utilized in recovering and re-uslng heat in a process carried out at elevated temperatures, rather than for the recovery and re-use of refrigeration as described.

It will frequently be most efficient in practice to separate the treated fluids from the heat absorbent material before complete thermal equilibrium is established. In such cases, the temperatures of the two streams leaving the separating zones, for example, will differ by from one or two to fifty or even more degrees Fahrenheit. The closeness to which temperature equalization is approached will of course be dependent upon economic factors involving equipment capacities, heating or cooling costs, etc., for any particular process. Generally when a powdered heat carrier is utilized, the heat transfer is sufficiently rapid that thermal equilibrium is substantially accomplished in a very short time.

The invention, although particularly applicable thereto, is not necessarily limited to the conversion of hydrocarbons, or even to processesinvolving chemical reactions. It may be used to advantage in various situations wherein an eilicient heat transfer or rapid cooling, or rapid heating,or all are desired.

One mode oi' operation which may be used quite advantageously in some cases is to introduce the mobile heat retentive or absorbent material into contact with fluids to be heated or cooled at a plurality of points spaced along the line of flow. Thus, several streams of heat absorbent may enter a heat transfer zone at different points, and then flow either concurrent with or countercurrently to the said fluid. In this way the amount of heat transfer occuring at all points in the heat transfer zone is readily controlled. The quantity and/or temperature of the heat absorbent introduced may vary `from one point of introduction to another.

It is to be understood that various heat retentive materials are not necessarily equivalent in effectiveness or applicability to a `given process. The particle size of solid material used, its heat capacity, its heat conductivity, its mechanical strength and resistance to comminution or agglomeration, and its stability at the temperature to be encountered are among the most important factors to be considered in choosing a solid heat absorbent for use in a particular process. It will also be appreciated that a powdered solid and a solid of relatively large particle size are not necessarily equivalents, for each form has among its y advantages some not possessed by the other, with intermediate particle sizes .having such advantages in proportion to their approach to one or the other extreme.

I claim:

1. A continuous method for bringing an organic fluid to a conversion temperature, effecting a desired conversion thereof, and then rapidly altering the temperature thereof and recovering a substantial amount of the heat or cold imparted thereto, which comprises continuously passing a stream comprising such an organic fluid serially through a first heat transfer zone, a second heat transfer zone, a conversion zone, and a third heat transfer zone, continuously 'passing a stream of solid mobile heat absorbent through a closed circuit including said flrst and third heat transfer zones, continuously maintaining the temperature of said stream of solid heat absorbent entering said rst heat transfer zone at a level different from that of said stream of organic fluid entering said first heat transfer zone, continuously maintaining said organic fluid and said solid heat absorbent within said first heat transfer zone in intimate contact for a sufficient time to alter the temperature of said organic fluid toward said conversion temperature by direct heat exchange between same and said heat absorbent, continuously further altering the temperature of said organic uid in said second heat transfer zone to bring same to said conversion temperature, continuously maintaining said organic fluid in said conversion zone at said conversion temperature under conditions effecting the desired conversion thereof, and rapidly and intimately contacting within said third heat transfer zone said organic fluid eilluent from said conversion with said heat absorbent in such quantity and at such a temperature as to rapidly alter the temperature 17 of the conversion eiiiuent rluld away from said conversion temperature and to recover at least a portion of the heat or cold imparted to said organic fluid in said second heat transfer zone by direct heat exchange between said fluid and said heat absorbent.

2. In the production of butadiene by the hightemperature conversion of hydrocarbons, the improvement which comprises rapidly effecting a suspension of silicon carbide particles smaller than about 60 mesh in a hot gaseous stream of butadiene-containing conversion effluents, said particles being at such a, temperature and in such quantity as to cool said eiiluents to a temperature at least as low as about 700 F. at which undesired reactions are inhibited in a period of time less than about one second, separating the resulting suspension of powdered silicon carbide in gases into heated silicon carbide particles and quenched gases, recovering butadiene from said quenched gases, suspending said heated silicon carbide particles in cool fluid hydrocarbon feed to said conversion to partially heat said feed and to cool said silicon carbide powder, separating the resulting suspension into heated feed and cooled silicon carbide particles, and again utilizing the latter for said quenching.

3. A method according to claim 1 wherein said organic fluid is heated in said rst and second heat transfer zones and is cooled in said third heat transfer zone.

4. A method according to claim 3 wherein an unsaturated hydrocarbon material is produced by conversion of an organic fluid at elevated temperatures.

5. A method according to claim 3 wherein said organic fluid is quenched in said third heat transfer zone by intimate contact with said solid mobile heat absorbent in finely divided form.

6. A method according to claim 1 wherein said organic fluid is cooled in said rst and second heat transfer zones and is heated in said third heat transfer zone.

'7. A method according to claim 6 wherein said conversion is a. polymerization reaction.

8. In the production of acetylene by the hightemperature conversion of hydrocarbons, the improvement which comprises rapidly effecting a suspension o silicon carbide particles smaller than about 60- mesh in a hot gaseous stream of acetylene-containing conversion eflluents, said particles being at such a temperature and in such a quantity as to cool said eiiluents to a temperature at least as low as about 1,000 F. at which undesired reactions are inhibited in a period of time less than about 0.2 second, separating the resulting suspension of powdered silicon carbide in gases into heated silicon carbide particles and quenched gases, recovering acetylene from said quenched gases. suspending said heated silicon carbide particles in cool iiuid hydrocarbon feed to said conversion to partially heat said ieed and to cool said r 18 silicon carbide powder, separating the resulting suspension into heated feed and cooled silicon carbide particles, and again utilizing the latter for said quenching.

9. In the production of highly reactive organic materials by the high-temperature conversion of organic uids, the improvement which comprises rapidly effecting a suspension of silicon carbide particles smaller than about 60 mesh in a hot gaseous stream of conversion eiiluents containing said highly reactive organic material, said particles being at such a temperature and in such quantity as to cool said effluents in a. suiiiciently short period of time to a suiciently low temperature to inhibit undesired reactions, separating the vresul-ting suspension of powdered silicon carbide in gases into heated silicon carbide particles and quenched gases, recovering said highly reactive organic material from said quenched gases, suspending said heated silicon carbide particies in cool fluid organic feed to said conversion to partially heat said feed and to cool said silicon carbide powder, separating the resulting suspension into heated feed and cooled silicon carbide particles. and again utilizing the latter for said quenching.

10. A method according to claim 3 wherein said solid mobile heat absorbent comprises particles of fused alumina.

11. A method according to claim 1 wherein said organic fluid passes countercurrently to a stream of solid mobile heat absorbent in particulate form in said rst and third heat transfer zones.

12. A method according to claim 11 wherein said organic fluid is contacted with refrigerated aluminum spheres as said heat absorbent at temperatures below normal.

JOHN D. UPHAM.

REFERENCES CITED UNITED STATES PATENTS in the Number Name Date 1,148,331 Olsson July 27, 1915 1,178,667 Niewerth Apr. 11, 1916 1,973,851 Feiler et al Sept. 18, 1934 1,977,684 Lucke Oct, 23, 1934 2,197,257 Burk Apr. 16, 1940 2,289,329 Prickett July 7, 1942 2,303,047 Hemminger Nov. 24, 1942 2,322,122 Frolick et al June 15, 1943 2,366,805 Richker Jan. 9, 1945 2,376,190 Roetheli et al May 15, 1945 2,391,555 DeSimo et al Dec. 25, 1945 FOREIGN PATENTS Number Country Date 60,147 Norway Nov. 21, 1938 525,197 Great Britain Aug. 23, 1940 Certificate of Correction Patent No. `2,443,210. l June 15, 1948. y,

vJOHN D. UPHAM It is hereby-certified that errors appear in the printed specification of the above numberedpatent requiring correction as follows: Column 2, line 46, for a before thev Word temperatures read at; column 3, line 32, for butene read butenes column' 8, line 51, for temperature read temperatures; column 13, line 23,A for great read greater; and that the said Letters Patent should be read with these corrections therein that the same may co orm to the record of theecase in the Patent Office."` x

Signed and sealev this 16th day of November, A D. 1948.

THOMAS F; MURPHY,

Assistant Uommzssoner of Patents.

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