US2931843A - Pyrolytic conversion of hydrocarbons employing a molten metal as a heat transfer medium - Google Patents

Description

F. J. BRUNS April 5, 1960 2,931,843 PYROLYTIC CONVERSION OF HYDROCARBONS EMPLOYING A MOLTEN METAL AS A HEAT TRANSFER MEDIUM Filed Jan. 11, 1956 2 Sheets-Sheet l INVENTOR FRANK J. BRUNS BY a, W yf df y F. J. BRUNS April 5, 1960 2,931,843 7 PYROLYTIC CONVERSION OF HYDROCARBONS EMPLOYING A MOLTEN METAL AS A HEAT TRANSFER MEDIUM 2 Sheets-Sheet 2 Filed Jan. 11, 1956 INVENTOR *FRA K J. mums w W'C t ORNEY a gaseous conversion'products whereby the products PYROLYTIC CONVERSION OF HYDROCARBONS EMPLOYING A MOLTEN METAL AS A HEAT TRANSFER MEDIUM Frank J. Bruns, Hazel Crest, Ill., assignor to Sinclair Refining Company, New York, N.Y., a corporation of Maine Application January 11, 1956, Serial No. 558,583 2 Claims. (Cl. 260-683) 'This invention relates to the art of pyrolysis and in particular is concerned with apparatus and a method for the pyrolysis of hydrocarbons, especially low molecular weight gaseous hydrocarbons, employing a molten metal such as lead as a heat transfer medium.

The pyrolytic conversion of hydrocarbons to more valuable products, including methods and appropriate apparatus, is a known art in the petroleum industry. For example, hydrocarbons can be converted to acetylene, a materlai useful as such and also useful as a raw material for the manufacture of various other chemicals such as aromatic hydrocarbons. To produce acetylene from hytirocarbon gases such as ethane, temperatures in excess of 2000 F. are used. By employing the same processing steps at a lower temperature, say or 1000 to 1200" F., the produced acetylene is, upon production, polymerized to benzene and other normally liquid hydrocarbons. The production of ethylene from propylene occurs at temperatures of about 1200 to 1800 F., and polymerization of ethylene to aromatics occurs at about the same temperatures.

Apparatus to effect these conversions commercially includes the well-known pebble heaters. ble heater apparatus, reactors containing molten metal as a heat exchange material are known and apparently have found limited commercial use. Problems encountered in use of molten metal reactors, in addition to the obvious danger inherent in handling heated materials of this nature, have included corrosion from metal splattering under the influence of the gases present, difliculties in introducing reactants into molten metal, the disadvantages of batch processes magnified by solidification of coke and tars in the metal mass and so on. The present invention in particular relates to pyrolysis apparatus and a method employing molten metal as the heat exchange material.

it has now been discovered that pyrolysis of hydrocarbon materials can be effected in an economical manner in a newly devised apparatus comprising a vertically elongated closed ended reactor provided with a body of molten metal in its lower end portion, inlet means for reactants, outlet means for product eifiuent, means to cool and circulate the heat exchange material from the bottom to the top of the reactor and means to facilitate continuous removal of excesscoke and tars accumulating during the course of pyrolysis. Chemical conversions are carried out in accordance with the present method invention for chemical conversions by passing a feed stock into a body of molten metal whereby conversion takes place and tars and coke form and accumulate on the surface of the metal, continuously withdrawing a portion of the molten metal and cooling it, reintroducing the cooled metal into an upper portion of the reaction zone and passing it downwardly into contact with the rising are quenched and scrubbed of entrained tars and coke. The largest portion of the coke and tars produced during conversion float to the surface of the body of molten metal 'where they collect and serve to m ze .b P Pg and In addition to pebnited States atent C high specific heat.

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splattering of the metal under the influence of the feed stock and reaction products. As excess coke and tars accumulate, a portion is continuously withdrawn; this portion advantageously is about equivalent to that amount which is being formed after a layer is built-up so that substantial equilibrium is maintained with respect to coke and tar build-up. The present invention thus provides apparatus and a method for chemical conversions such as pyrolysis in the presence of molten metal which, in addition to minimizing many of the disadvantages of prior art apparatus and methods, is capable of substantially continuous use rather than being limited to batch operation.

The invention will be more easily understood by refer- :ence to the attached drawings in which: 15

Figure 1 shows an apparatus, partly in section and partly in elevation, including a reactor of the present invention; and

Figure 2 shows a detail of a feed injector means; and

Figure 3 shows a detailed check valve type spray means which can be employed in the present invention; and

Figure 4 shows a second embodiment of a spray means which can be employed in the present invention.

Referring now to the drawings, the numeral 10 repre sents a reactor advantageously having a generally circular horizontal cross section. In the embodiment shown, the upper portion 12 of reactor 10 is of smaller crosssectional area than the lower portion 14. The reactor is constructed of a heat resistant material, such as steel, and is lined internally with a suitable material such as an alloy steel or a refractory capable of withstanding elevated temperatures and the leaching effect of a molten metal such as lead. A body of molten metal 16 is disposed in the lower portion 14 of reactor 10. Lead is the preferred metal to be employed; other metals can be used if they are molten at processing temperatures and melt below l0O0 F., boil at over 2000 F. and have a The metal is maintained in molten condition by any means desired for purposes of conducting the reactions. Suitable means include indirect heat exchange means such as a tube bank 18 containing a heat exchange material, for example, hot gaseous combustion products. Suitable auxiliary equipment such as a burner means 20, a vent 21 for combustion products and molten metal in the reactor is an overflow means 22 to permit continuous removal of coke and tar which accumulate during reaction. Advantageously means 22 can take the form of a weir or other device operating upon overflow and is located, to advantage, along the periphery of the vessel 10 when considering its inner surface. Normally a single overflow means will suflice for most reactions but more than one can be employed where desired. Means 22 is spaced above the body of metal a distance correlated with other variables in the system such as metal volume, feed rate and so on; in general, a distance of about 3 to 10 inches between the top of the overflow means and the surface of the metal will be satisfactory. A conduit 24 communicates with the coke removal means 22 to conduct coke to suitable disposal or use facilities (not shown). The conduit 24 can be prow an electromagnetic pump.

temperature, i.e., about 1500' eratmg temperature,-the apparatus'ispurged with a'hot length defining an annular space 35 between the valve means 36 and conduit 34. The valve means 36 is, to advantage, automatically operated and to this end means 36 is attached to a head 40 which'withdraws' means 36 under the influence of the pressureof feed entering through entrance 4-1. By having the valve operated on pressure from the feed gas, molten metal is"prevented from flowing into the feeding mechanism at all'times since the entrance will be closed by the valve when feed is stopped and by the pressure of gas during feed injection. Each feed injector means 30 is, to advantage, provided with individual insulation 38 to "protect the'c'onduit 34 from the adverse influence of 'the molten metal 'within the reaction vessel and to prevent coke formation in "the annular space 35. As shown in'Figure l the injectors are supplied by a common header 42 positionedexternally of the reactor to facilitate easier maintenance. Feed is fed to the header 42 and the injector'means 30 from a source (not' shown) 'through a common conduit 63; for heat economy, the feed stock is heat exchanged in'a heat exchanger 68 with molten metal withdrawn from the reactor. The disposition of header 42 externally of the reactor in conjunction with the insulation and physical characteristics of the feed injector means, that is, the provision of the small annular space 35 for feed injection at high velocity and low residence time, serves to prevent coking contamination in the feed system since cracking does not take place there.

In the upper end of the smaller portion 12 of the vessel 10 a cyclone separator 46, or equivalent means, is

provided to permit separation of entrained tars, coke' and the like remaining in the product at that point. An outlet means 48 communicates with thecyclone'sepafat i 45 andserves to conduct product efiiuent through hea xchanger 19 and to the recovery system (not strewn A plurality of means50 are disposed in the upper end portion 12 of vessel 10 below the separator means 46. Means 50 are adapted to spray molten metal downwardly into contact with rising gaseous efiluent. Means 50 can take a form as shown in Figure 3 which comprises an inlet conduit 52 provided with a ball valve 54 which has a spring load 56 and is supported by a bracket 58. Another advantageous embodiment for the means '50 can be themore simple form of Figure '4 comprising a conduit 60 provided with a splatter plate 62 attached-bya suitable bracket 64. Molten metal'is suppliedto a header 51 communicating with spray means'50by being withdrawn from the bottom portion 14 ofvessel 10 through a suitable conduit 66, is heat exchanged with the 'feed stock in exchanger 68 and pumped to the spray means header 51 by use of a means 70 which, to advantage, "is In normal operation, about 2 to 10 weight percent is continuously withdrawn, cooled and reintroduced in the reactor vessel 10 through the spray means 50; the optimum amount of metal circulated externally of the reactor and used for spraying will depend primarily upon the metal employed, the amount of scrubbing desired, the efliciency of the spraying device, heat content considerations and so on.

In operation, for example. for the pyrolysis of propane. hot gases are passed through the heater tube bank to melt the metal, for example lead, and raise it to operating F. Upon attaining "opinert gas such as nitrogen by passingheated nitrogen into the reactor through the feed system-i Purging is accomplished to remove oxygen from the entire system including the lead bath, and to heat the entire apparatus to conditions approaching those obtained during operation. When the system is completely purged, the supply of purging gas is cut-01f and feed gas, for example, C. P. propane or a refinery propane fraction, is'cut into the ifeed line 63 and enters the body of molten metal in the reactor. In passing through the molteri'leadbathqthe feed gas is quickly heated to reaction temperatures and 4 cracking occurs and is accompanied by coke formation and some polymerization of the cracked products. The coke formed passes through the bath with the product gases and the majority of it, especially that which is dry and powdery in form, collects and floats on the surface of themolten lead.

' During operation a portion of the body of molten lead is withdrawn from the reactor, heat exchanged withcolder feed gas, and pumped to the topof the reactor. Where heat exchange with feed gas and residence time external of the reactor is insuflicienttocool thecirculating lead to below about 1000 F., additional cooling means such as cooling coils about the conduit can be employed. At the top of the reactor the withdrawn lead' is introduced in 15 a manner so that the lead is sprayed downwardly into contact with gases rising from the top of the lead bath. Product gases rising from the body of molten metal normally entrain part of the coke and-tars .which form during'reaction-These impuritiesare scrubbed from the gases by-the sprayed lead which serves the additional "functions of quenching the gases to prevent further re action and washing the reactor walls to remove coke. *The cleaned and quenched gases leave the reactor after passing through a means such as a cyclone separator and are passed to a product recovery system.

As pointed-out above, coke forms during reaction and iii-large part collects on the surface of the lead bath. This coke serves in part to pacify the surface of the bath andin part to scrub gases passing through it. To operate -the sys'tem' continuously, it is essential that coke be re *rnove'd'before it builds up to the point where it would be excessive- To'eifect coke removal, a weir 22 or similar skimming means operating onoverflow is provided above the surface of the metal, and as excess coke accumulates it isthn's' continuously removed from the reactor by passin'g'ovef-the' wei'r and out of'the zone of reaction. The-feedrate chosen for a given conversion in a reactor of specified dimensions is largely determined by "volume of the molten metal and void volume. Since 40 bubbles riseat a constantvelocity, increasing the lead depth would serve to increaseresidence time at reaction -temperature. Void volume must be such so that sulficient time and space are allowed for adequate scrubbing o'f product' gases rising from. the molten metal. For a reactor-of-8 inch pipe (7.625 in I.D.), using a lead -bath l6 i'nches deep (0.55 cu. ft.) and a void space above -'the-bath of-0!79 cu.-ft., whereinpropane is to be cracked at temperatures of about 1500 F., a feed rate of about 'Sto -30 c.f.h. will give satisfactory results and provide ample agitation-and contact oflead with the heater tubes toprovide uniform bath temperatures and avoid excessive bumping and splattering which would contribute to lead los's.- To provide a lead bath temperature of about 1500 FRI-I1 the described system, hot combustion gases at about '1900'F. in theheater tubes would be required. Feed which is heat exchanged with withdrawn metal generally is at a temperature of about 800 F. upon entering the reactor. Quenched product generally leaves the reactor at a temperature of about l000 F.

-In'a typical run in theabove described reactor employing C.P.' propanetanalyzing at 97.5% propane), a leadtemperaturemaintained within 1500 to 1530" F., and employing a feed rate of about 2.6 pounds per hour, --a test----was conducted fora-period of about ten hours. -Ethyle'ne-resulted in an amount, based on the total feed, ---of about 32.4;weight percent,a significant yield. Liquid *yield (polymerizedproduct) was less than 10 weight percent thereby demonstrating the effectiveness of the metal spray in minimizing degradation reactions.

What is claimed is:

H li 'Amethod of conducting chemical conversions at high temperatures whichcomprises maintaining a body "of molten metal atan elevated conversion temperature in"thelowjer portion of a reaction zone, passing a feed stock containing carbon and hydrogen into said body of molten metal whereby conversion takes place, and product and coke and tars are produced, continuously collecting coke and tars on the surface of said body of metal, removing from the reaction zone at the location of collection a portion of the accumulated coke and tars to prevent excessive build-up, continuously withdrawing a portion of said molten metal, cooling said withdrawn portion of metal and reintroducing the cooled metal into an upper portion of said reaction zone by spraying said metal downwardly into contact with rising conversion products whereby said conversion products are quenched and scrubbed of entrained tars and coke, and recovering said quenched and scrubbed products.

2. The method of claim 1 wherein a layer of the coke and tar is continuously maintained floating on the body of molten metal.

References Cited in the file of this patent UNITED STATES PATENTS 1,141,529 Danckwardt June 1, 1915 1,838,029 Isles Dec. 22, 1931 2,431,455 Blanding Nov. 25, 1947 2,448,922 Simpson et al. Sept. 7, 1948 2,508,120 Lonngren May 16, 1950 2,543,743 Evans Feb. 27, 1951 2,780,587 Watkins Feb. 5, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,931,843 April 5 1960 Frank .Io Bruns It is herebj certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4L line 71 for chemical read hydrocarbon column 5 line 7 after "metal 'f insert from a point substantially below the surface of said body of metal Signed and sealed this 27th day of September 1960.,

(SEAL) Attest:

KARL H.a AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. A METHOD OF CONDUCTING CHEMICAL CONVERSIONS AT HIGH TEMPERATURES WHICH COMPRISES MAINTAINING A BODY OF MOLTEN METAL AT AN ELEVATED CONVERSION TEMPERATURE IN THE LOWR PORTION OF A REACTION ZONE, PASSING A FEED STOCK CONTAINING CARBON AND HYDROGEN INTO SAID BODY OF MOLTEN METAL WHEREBY CONVERSION TAKES PLACE, AND PRODUCT AND COKE AND TARS ARE PRODUCED, CONTINUOUSLY COLLECTING COKE AND TARS ON THE SURFACE OF SAID BODY OF METAL, REMOVING FROM THE REACTION ZONE AT THE LOCATION OF COLLECTION A PORTION OF THE ACCUMULATE COKE AND TARS TO PREVENT EXCESSIVE BUILD-UP, CONTINUOUSLY WITHDRAWING A PORTION OF SAID MOLTEN METAL, COOLING SAID WITHDRAWN PORTION OF METAL AND REINTRODUCING THE COOLED METAL INTO AN UPPER PORTION OF SAID REACTION ZONE BY SPRAYING SAID METAL DOWNWARDLY INTO CONTACT WITH RISING CONVERSION PRODUCTS WHEREBY SAID CONVERSION PRODUCTS ARE QUENCHED AND SCRUBBED OF ENTRAINED TARS AND COKE, AND RECOVERING SAID QUENCHED AND SCRUBBED PRODUCTS.

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