US3403181A - Pyrolysis process and apparatus for manufacture of ketenes and anhydrides - Google Patents

Description

P 6 E. 5. PA! ER ETAL 3,403,181 PYROLYSIS PROCESS AND PARATUS, FOR MANUFACTURE OF'KETENES AND, ANl-IYDRIDES Original Filed May 4, 1964 Y 3 Sheets-Sheet l v I pHAMBER v4 J KErE/VE our r0 CONDENSER Vanna 4 sracx';

3 bow/1v s. INT/5R .ROBERT ETREY JOHN -/-/L JENSEN. JR. INVENTQRS ATTORNEYS Sept. 24, 1968 E. s. PAINTER ET AL 3,403,181

PYROLYSIS PROCESS AND APPARATUS FOR MANUFACTURE OF KETENES AND ANHYDRIDES Original Filed May 4, 1964 3 Sheets-Sheet 2 PREHEA r SUPERHE/J 7" cRA GK/NG A CR4 CK/A/G CHAMBER CHAMBER CHA MBER CHAMBER STREAM- A 78 7 A DRAFT DRAFT .58 \56 54 RA scRuBBER as //6 62 v 92 '//0 CONDENSER I08 VAPOR PREssuRE :2: Q1 MEASURING pEv/cE K AIR OPERATED v VALVE FoR HOAC FEED CRUDE PRODUCT 4| IP OVERFLOW HEAT ExcH /vaER cooLER EDW/NS. PAINTER ROBERT c. PETRE) 7 JOHN H. JENSEN JR- INVENTORS ArmR/vEYs Sept. 24, 1968 E. s. PAINTER ET AL 3,403,181

PYROLYSIS PROCESS AND APPARATUS FOR MANUFACTURE OF KETENES AND ANHYDRIDES Original Filed May 4, 1964 3 Sheets-Sheet 5 EDWIN 5. PAINTER ROBERT C. PETRE) JOHN H. JENSEN JR.

INVENTORS By QMM ATTORNEYS United States Patent 3,403,181 PYROLYSIS PROCESS AND APPARATUS FOR MANUFACTURE OF KETEN ES AND ANHYDRIDES Edwin S. Painter, Robert C. Petrey, and John H. Jensen, Jr., Kingsport, Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Continuation of application Ser. No. 364,509, May 4, 1964, which is a continuation-in-part of application Ser. No. 31,441, May 24, 1960, now Patent No. 3,136,811, dated June 9, 1964. This application July 20, 1966, Ser. No. 566,712 The portion of the term of the patent subsequent to July 5, 1983, has been disclaimed 5 Claims. (Cl. 260-5855) ABSTRACT OF THE DISCLOSURE A system for preparing ketenes by pyrolysis of material in a furnace having interwound helical coils in its preheating and superheating chambers, with means for subsequent conversion to anhydride.

This application is a continuation of Ser. No. 364,509, filed May 4, 1964, now abandoned, which in turn is a continuation-in-part of Ser. No. 31,441, filed May 24, 1960, now U.S. Patent 3,136,811, issued June 9, 1964.

This invention relates to the manufacture of ketenes and anhydrides. More particularly, this invention concerns the manufacture of ketenes by the pyrolysis of acetic acid and the conversion of the ketene to acetic anhydride.

Our co-workers have disclosed various methods and apparatus for the manufacture of ketenes and anhydrides by pyrolysis of certain compounds such as acids, ketones, and other ketenizable materials. In U.S. Patents 2,258,985 and 2,393,778 they have described one and two-chamber furnaces and processes for pyrolysis of ketenizable organic compounds. In US. Patent 2,541,471 our co-workers have described a three-chamber furnace. Painter, one of the inventors herein, in U.S. 2,784,065 has disclosed another embodiment of a three-chamber furnace. Painter et al. in US. 2,776,192 have disclosed that superheating may be carried out on separate streams of the material to be ketenized. In Ser. No. 31,441, of which the instant application is a continuation-in-part and in which application claims have been allowed, we have described a fourchamber process and apparatus. According to said Ser. No. 31,441 separate streams of ketenizable material are preheated in different parts of the same preheating chamber, and then superheated in different parts of the same superheating chamber before being cracked in separate cracking chambers.

While all of the foregoing procedures of Painter and co-Workers have proved highly successful in the manufacture of ketenes, a new process and apparatus by which an equally good conversion to ketene and an as eflicient way of producing ketene may be achieved represents a highly desirable result. After extended investigation, we have found a process and apparatus whereby as great or greater efiiciency of production than heretofore known in the production of ketenes and corresponding anhydrides is provided.

This invention has for one object to provide apparatus and process of improved economy for manufacture of ketenes. A particular object is to provide an improved procedure for pyrolysis of acetic acid to ketene. Another object is to provide an economical manner of converting ketene to acetic anhydride whereby improved economy of construction, yield, and conversion may be secured. A special object is to provide an apparatus arrangement whereby ease of preparation of ketene may be increased. Still another object is to provide a novel apparatus arrangement and method for producing ketenes and anhydrides which permit an alternate construction capable of equal or more efiicient results. Another object is to provide an apparatus of the class indicated wherein there is provided a special coil arrangement. Other objects will appear hereinafter.

In the broader aspects of our invention we have found that in a four-chamber furnace made up of two cracking chambers in parallel connected in series with preheating and superheating chambers when two parallel interwound coils are used in both preheating and superheating cham bers we are able to use efiiciently substantially all of the heating gas with a minimum amount of waste heat. By such an arrangement we are also able to control the temperature from top to bottom of each chamber without undue variation. In further detail, two separate streams of material to be cracked enter the top of the preheating chamber and wind around in parallel paths in a helicalshaped coil arrangement until they reach the bottom of the chamber. Then each separate stream is preferably carried upward along the vertical axis of the core formed by the coils and then conducted through the superheating chamber in a similar manner. One stream then passes through a single coil in one of the cracking chambers and the other stream passes through a similar coil in the other cracking chamber before the two streams join as one for the contacting of the ketene with acetic acid to produce acetic anhydride. The coil arrangements in the two parallel cracking chambers which have the separate streams of ketenizable material introduced from the preheating and superheating chambers are of similar construction to the preheating and superheating chambers with the principal exception that there is only one coil in each rather than two parallel coils in each.

We have also found by one embodiment of our invention that we may control the composition of the anhydride-acid process stream for efiiciency in converting ketene to anhydride by withdrawing sample streams of the ketene-acetic acid reaction product and using a dilferential vapor pressure transmitter to.compare the vapor pressure of the acetic anhydride process stream to the vapor pressure of a standard solution such as methyl Cellosolve. The measure of the difference between the two is transmitted to a control station which operates a pneumatic valve on the acid feed and controls the amount of acid introduced to the anhydride unit.

A further understanding of our invention may be had from a consideration of the attached drawing forming a part of the present application.

FIG. 1 is a semidiagrammatic side elevation view in section illustrating a four-chamber furnace embodying the coil arrangement of the present invention. As will be apparent hereinafter, since many of the details of construction may be the same as presently used construction for such type of furnaces, extended description of FIG. 1 will not be necessary.

FIG. 2 is a more fully diagrammatic side elevation view in a particularly simplified form for illustrating the piping and coil arrangement in a four-chamber furnace of the present invention. This figure has been presented in particular to illustrate the basic inventive features of the instant invention.

FIG. 3 is a semidiagrammatic side elevation view of an anhydride forming unit such as may be used in conjunction with the furnaces of the present invention. That is, the ketene produced in the furnaces of the present invention may be utilized in the process and apparatus of FIG. 3 for the production of a uniform anhydride product.

FIG. 4 is an exploded view of coils 74 and 76 of the preheat chamber of FIG. 2 with coils pulled apart somewhat to show their parallel winding construction in somewhat more detail. These coils are similar in construction to coils 82 and 70 of the superheat chamber.

Referring now to FIG. 1, it can be noted that many of the parts shown in this figure may be the same or similar to the parts described in abovementioned companion Patents 2,541,471; 2,784,065 and 2,776,192 and co-pending US. patent application Ser. No. 31,441 and that the materials of construction may be the same as described in these patents and in this co-pending application. The furnace is comprised of a furnace housing which would be of suitable ceramic or brick work for enclosing the coils for preventing heat escape and also for bringing the heating medium in close contact with the coils. The interior of this furnace housing is divided. into four chambers 12, 14, 16 and 18. Each of these chambers is separated from the other chambers by suitable baffle walls 20, 22, 24 and 26. These ceramic bafile walls may be of any desired construction such as the various constructions disclosed in the patents and co-pending application just referred to. Chamber 18 is provided with an exit 28 whereby the heating gases may be exhausted to a stack (not shown).

In the construction shown in FIG. 1, the combustion chamber 30 is provided with one or more burners 32. However, supplemental to or in lieu of the combustion chamber, individual burners may be inserted into each of the chambers 12, 14, 16, etc. In such arrangement the burners are preferably positioned to discharge tangentially to the Walls and not to impinge directly on the coils in the chamber. Similar remarks apply to burner 34 in that it would be angled so as not to impinge directly on the parallel-aligned coils 36 and 38.

In addition to the refractory bafiies and the like just referred to, in at least chambers 12 and 14, and if desired, in the other chambers, there would be provided refractory core members such as 40 and 42 which core members are encircled by the cracking coils to be described in more detail hereinafter. Extended description of these core members, which may be solid or tubular, is unnecessary inasmuch as the construction thereof may be substantially exactly in accordance with the disclosure in companion US. Patent 2,541,471.

In each of these chambers of the four-chamber furnace there are positioned coils and piping through which is fed the ketenizable material to be cracked or pyrolyzed to the ketene. That is, cracking coils 44 and 46 are positioned in chambers 12 and 14. superheating and preheating coils 48, 50, 36 and 38 are positioned in the other two chambers 16 and 18. A further understanding of this coil arrangement and positioning, which is an important part of the present invention, will be had from a consideration of FIG. 2 which will now be described.

In this schematic and simplified view of FIG. 2, it will be observed that there has been provided the areas 52, 54, 56 and 58 corresponding to the four chambers referred to above. Such areas or chambers have been further identified by the legends appearing on FIG. 2 as cracking chamber, superheating chamber and preheating chamber.

In connection with the cracking chamber it will be noted that in addition there has been designated the capital letters A and B corresponding to stream A and stream B noted on the left of FIG. 2. In the arrangement of the present invention the piping and coil construction is such that two streams, namely A and B of the ketenizable material may be fed through the four chamber furnace simultaneously, the two streams joining at point 60 to leave the furnace through the single conduit 62.

Chambers 52 and 54 each contain a cracking coil 64 and 66 piped in parallel.

Considering cracking coil 64, this is connected by conduit 68 to the superheat coil 70, which superheat coil is connected by conduit 72 to the preheat coil 74. This preheat coil leads alongside parallel coil 76 in a spiral course back through conduit 78 to the feed (stream A) of the ketenizable material.

In a similar manner, cracking coil 66 is connected by a conduit 80 to a superheating coil 82. It will be noted that this superheating coil 82 is positioned so as to follow a course parallel to the spiral course of coil 70 of line A. Such an arrangement is thought to provide optimum heat distribution.

Continuing further with the piping of stream B, it will be observed that the superheat coil 82 is connected by conduit 84 to the preheat coil 76 which coil leads into the feed of stream B through conduit '86.

From this simplified piping diagram it will be observed that two streams A and B of ketenizable material may be fed into the four-chamber furnace of the present invention so as to follow each other in a substantially parallel course in both preheating and superheating chambers before separating for each to pass through its own cracking chamber. In each instance each stream A and B is subjected to approximately comparable preheating and superheating treatment in the chambers 58 and 56. Then each of the streams A and B enters its separate cracking chamber 52 and 54 wherein the final pyrolysis takes place. The resultant pyrolysis products are united at point 60 to the single conduit 62 through which the pyrolysis products are conducted to a condenser and other treatments to separate and/or utilize the products.

We have discovered that the capacity of the furnaces of the class under description is limited both by pressure drop in the tubing and by heat input to the furnace. We have found that the new arrangement of the present invention providing parallel sets of preheating and superheating coils otherwise in accordance with the arrangement of FIG. 2 contributes to a reduced pressure drop for a given flow rate and an increase in feed. Expressed in another way, by the new piping arrangement of the present invention the pressure drop obtained is equivalent to or superior to the pressure drop obtained in prior art three coil furnaces and the four-coil furnaces shown in copending US. patent application Ser. No. 31,441.

Referring now to FIG. 3, we have disclosed process and apparatus by which the ketene produced by the present invention may be utilized. The ketene leaving the furnace through conduit 62 may be passed into a condenser 88, the condensables are withdrawn at 90. The ketene gas thus preliminarily treated passes through conduit 92 into scrubber 94. In this scrubber the ketene gas is contacted with a circulating stream of a mixture of acetic anhydride and acetic acid entering the scrubber through conduit 96.

Acetic acid is admitted to this scrubber system through the supply line 98 which supply line contains therein automatic valve 100. The reaction product of the ketene with the acetic acid Withdrawn from the bottom of the scrubber at point 102 is pumped by pump 104 through heat exchanger 106 and then through the orifice device 108. This device is associated with the control system 110 which is interconnected with valve aforementioned. The reaction product overflows from scrubber 94 through conduit 112.

The control device functions to measure automatically the difference between vapor pressure of the flowing stream which is by-passed through lines 114 and 116 and a control solution (not shown). Such measurements are based on the vapor pressure and the operation of valve 100 in response thereto permits the automatic control of the reaction product of the ketene with the acetic acid to an accuracy within :0.5%. This permits the utilization of the ketene for making an acetic anhydride of limited variation.

A still further understanding of our invention will be had from a consideration of the following examples which are set forth to illustrate certain of our preferred embodiments of operations.

Example I A furnace with the arrangement of coils of FIG. 2 was used for an interval of several weeks in the production of 115,000 pounds per day of acetic anhydride. The coil arrangement used resulted in reduction of the pressure drop through the furnace and thereby produced a better vacuum, thus accounting for increased efliciency of operation. We have also found it possible to use this coil arrangement in three-chamber furnaces such as those of aforesaid U.S. Patents 2,541,471; 2,784,065 and 2,776,- 192.

Example II The control arrangement shown in FIG. 3 was used to control the percent acid in the scrubber process of converting ketene to anhydride as shown above to an accuracy of :0.5% acid. Normal operator temperature rise analysis had a standard deviation of :0.85%.

To supply additional heat auxiliary gas-fired burners may be used in the first chamber, now known as the preheat or preheating chamber. The use of burners in such chamber increases the temperature of the flue gas leaving the furnace. As already indicated above, when burners are inserted in the chambers, they are preferably positioned so the flame will not impinge directly on the coils. The fuel gas usage according to our invention amounts to about 2.25 to 2.5 cu. ft. per lb. of anhydride.

According to our invention and further detail as may :be noted by reference to FIG. 2 stream A and stream B flow in parallel through the preheat chamber, superheat or superheating chamber and then stream A goes to the fourth chamber designated the A cracking chamber and stream B goes to the third chamber designated B cracking chamber. Stream A and stream B follow parallel coiled paths in both preheat and superheat chambers.

The hot combustion gases from the A cracking chamber leave this chamber at the bottom and enter the B cracking chamber at the bottom and leave at the top thereof. The waste gases leave the superheat chamber at the bottom and enter the preheat chamber. The preheat chamber coils have a shell inside the coil. The hot gases entering at the bottom of the preheat chamber travel upward around the coils and outside the shell and enter the shell at the top of the chamber and travel down past the draft damper on to the steam generator and the waste gas stack. Gas burners may be fired in the annular space around the coil in the preheat chamber supplying additional heat.

For feeds A and B we used glacial acetic acid of approximately 99.95% purity. The acetic acid, as it entered the perheat chamber of FIG. 2, had injected therein a small amount of catalyst. That is, there was incorporated in the acetic acid feed a small amount of phosphate catalyst. Suitable catalysts are trimethyl phosphate, tri-isopropyl phosphate and tripropyl phosphate and other phosphate esters of this type. Streams A and B which are in series in the preheat and superheat chambers were subject to a temperature in the preheat chamber within the range of 600-1000 C. In the superheat chamber the temperature range was within the range of 750l500 C.

In the cracking chambers where the coils are in parallel arrangement, the temperature was within the range of 750l500 C. The heat was supplied by several burners positioned in all the chambers as needed to supply sufficient heat by burning natural gas to maintain the temperatures specified aforesaid in the respective chambers.

The pressure drop with the piping and coil arrangement of the present invention, from the point of entry :before the feed of the preheat zone to the exit at conduit 62 was of the order of 240 mm. As may be noted, such pressure drop is relatively low and compares favorably with the pressure drop of two and three and other fourchamber furnaces.

The rate of feed of the glacial acetic acid to the process in each separate line in accordance with Example I was of the order of 2700 lbs. per hour. The conversion of such feed to ketene was of the order of -85%.

The ketene produced in accordance with Example I was reacted with acetic acid in an apparatus as diagrammatically disclosed in FIG. 3 to give a high quality uniform acetic anhydride. As described above in connection with FIG. 3, the reaction of the ketene and acetic acid is controlled by continuously withdrawing a sample stream of the reaction product and measuring the vapor pressure by means of a differential vapor pressure transmitter and controlling the acetic acid flow by means of a controller obtainable commercially from Foxboro and other companies. By such controlled reaction wherein the feed of the acetic acid reacted with the ketene is controlled by the vapor pressure of the reaction product, there was obtained a very uniform acetic anhydride.

Although the process has been described primarily with respect to the conversion of acetic acid to ketene, this being one of the principal types of conversions carried out commercially, our process and apparatus may be utilized in the pyrolysis of other ketenizable materials exemplified by acetone, ethyl acetate, propionic acid and oher ketones and acids of this type.

It is thought apparent from the foregoing that we have provided a new and improved piping and coil arrangement which is specially adapted for four-chamber furnaces for the production of ketenes and anhydrides whereby increased economy is made possible with equal or better yields than heretofore possible. Also, we have shown how to control the uniformity of the acetic anhydride produced from ketene resulting from pyrolysis of acetic acid.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it 'will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A pyrolysis process using preheating, superheating, and separate pyrolysis zones, said process comprising the steps of:

(1) preheating two streams of material to be pyrolyzed by passing said streams through interwound helical paths in said preheating zone,

(2) superheating the preheated streams by passing them respectively through interwound helical paths in said superheating zone, and

(3) pyrolyzing said superheated streams by passing them respectively through helical paths in separate pyrolysis zones.

2. The invention of claim 1 wherein said preheated streams are treated in helical paths of substantially the same length, said superheated streams are treated in helical paths of substantially the same length, and wherein said material is ketenizable and said pyrolysis process produces ketenes.

3. An apparatus for pyrolyzing a stream of material comprising, in combination:

(1) a furnace housing;

(2) a first pair of interwound helical coils of tubing arranged in a preheat chamber defined by said housmg;

(3) a second pair of interwound helical coils of tubing arranged in a superheat chamber defined by said housing;

(4) two separate helical coils of tubing arranged in separate pyrolysis chambers defined by said housing;

(5) first conduit means for serially connecting one coil of said first pair to one coil of said second pair, and connecting the other coils of said first and second pair;

(6) second conduit means for serially connecting one coil of said second pair to one of said separate coils, and connecting the other coil of said second pair to the other separate coil; and

(7) said coils of tubing and said first and second conduit means providing a flow path for sal'i'i stream of material.

4. The invention of claim 3 wherein said first and second pair of coils extend from substantially the top to the bottom of their respective chambers.

5. The invention of claim 4 wherein said first conduit means extends from the bottom of said first pair of coils,

through the core formed by said first pair of coils, and to the top of said second pair of coils.

References Cited UNITED STATES PATENTS 2,776,192 1/1957 Painter et a1. 23277 2,784,065 3/1957 Painter 23--277 2,541,471 2/1951 Hull et a1. 23-277 2,967,515 1/1961 Hofstede et al. 165-145 X 3,259,469 7/1966 Painter et a1. 63 277 JOSEPH SCOVRONEK, Primary Examiner.

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