US2623011A - Preparation of olefins by particulate coal carbonization - Google Patents

Description

Dec. 23, 1952 A; J. WELLS 2,623,011

PREPARATION OF OLEFINS BY PARTICULATE COAL CARBONIZATION Filed Nov. 30, 1946 E 1 3 H 0 q .3 M S E 17-- a g g :2 Q I g 4 3: i 8 4 I! a if .PRflflVCT 6455s I .4 INVENTOR.

Adoizzmm J Wells Patented Dec. 23, 1952 PREPARATION OF OLEFINS BY PARTICU- LATE COAL CARBONIZATION Adoniram J. Wells, Wilmington, Del., assignor to E. I. du Pont de Nemours 8; Company, Wilmington, DeL, a corporation of Delaware Application November 30, 1946, Serial No. 713,374

1 Claim.

This invention relates to an improved process for the preparation of unsaturated hydrocarbons, and more particularly, the preparation of ethyl ene by the carbonization of coal.

For a number of years an eifort has been made, in the preparation of illuminating gas by the coking of coal, to provide a high percentage of illuminants and of the illuminants the olefins are the most effective. Attempts were made to increase the illuminants in coke-oven gas but, due in no small measure to the time lag in heating the coal to carbonization temperatures and long-drawn out temperature cycles inherent in such processes, rewards were meager. Furthermore, the difficulties of heat transfer have limited gas production, because of the wide temperature difference often existing in the coke ovens. At any one time the temperature gradients through the carbonizing chamber are quite sharp, a typical condition being that the temperature of the fully coked material near the heating wall will be about 1000" 0., while the uncoked coal in the center will be about 100 C. Inasmuch as the production of gas from coal is, by and large, a chemical process and as chemical processes even of the simpler types require careful and accuratetemperature control for the production of maximum yields of a given product, it follows that modifications of coke-oven technique would not be expected to realize the maximum yields of gas from coal, with no expectation of directing the course of the operation to give maximum yields of particular products such as olefins.

An object of the present invention is to provide an improved process for the preparation of olefins by the carbonization of carbonaceous materials. Yet another object is to provide a process for the carbonization of coal in particulate form, whereby the optimum temperatures for olefin production are realized. A further object is to provide a process for the coking of powdered coal, wherein high gas production to olefins is realized by coking the coal from the fluidized state. Another object is to provide a process for coking powdered coal, wherein uninterrupted flow of the coal and coke through the coking zone is maintained. Other objects and advantages of the invention will hereinafter, appear.

In its broader aspects the invention involves pulverizing coal or other solid carbonaceous material, such as peat, oil shale, and the like, and while dispersed in a fluid medium, subjecting it to high-temperature carbonization. In counterdistinction to coke-oven operation, wherein a large mass of coal is externally heated, requiring a long time to raise the temperature of the mass Cl. 202l7) to carbonization temperatures, the process of the instant case substantially instantaneously brings the coal to the optimum temperature for carbonization. Research has shown that it is necessary, in order to reach the objective of maximum olefin yields from coal, to reduce to a minimum the time the olefin is at coking or carbonization temperature. With such requirements, coke ovens were obviously unsuited for maximum olefin production. The process of the instant case permits accurate reaction time and temperature controls, thereby making it possible to realize the objective.

By mass spectrometric analysis it has been found, that when carbonizing coal of smallparticle size, the maximum amounts of olefins are evolved at temperatures below 1000 C. If the desired olefin is ethylene, temperatures between 800 and 950 C. are best, with a preferred range between 850 and 900 C. If propylene is the desired olefin, the optimum range is between 700 and 850 C. while if acetylene is the desired unsaturate, high temperatures are called for, viz. 900 to 1200 C.

In addition to controlled temperature for carbonization, the amount of olefin or acetylene recovered is determined also by the time they are in the carbonization zone at temperature. No matter what method of heating is employed, the unsaturated product gases should be removed from the hot carbonization zone in less than 3 seconds after separation from the coal. If an externally fired reaction zone is used, the time should be within 0.2 and 1.0 second; if a condensable gas is used to provide the heat, the time should range between 0.2 to 2.0 seconds; and, if a boiling bed is used, a time between 0.5 and 3.0 seconds.

There is a third variable which must be controlled to realize the greatest evolution of the unsaturated hydrocarbons from coal during its carbonization and that is the particle size of the coal being carbonized. If the externally fired reaction zone is used, described below, a 20-mesh size (1. e. a coal that will all pass through a screen having 20 holes per linear inch) is the largest that will give optimum product yields, with the best yields with a size of about mesh. When using a heating condensable fluid, sizes between 50 and 100 mesh may be used but, preferably, a 100-mesh size or smaller; while with a boiling bed zone, sizes of 100 mesh or smaller are preferred.

The powdered coal may be heated by any suitable means, the coal being, e. g. dropped by gravity through the center of an externally fired tube which may or may not also contain a condensable or non-condensable gas that may flow cocurrent with or countercurrent to the flow of coal, the gas sweeping out the unsaturates formed. Alternatively, the boiling bed technique may be used, i. e. the powdered coal is carbonized in a boiling bed, the boiling being supplied by, for example, the introduction into the bed of a condensable or non-condensable gas, which may or may not supply the necessary heat to provide adequate carbonization. Other methods of heating the tubular reactor or boiling bed reaction will readily suggest themselves to those skilled in the art. Examples of satisfactory methods include external heating; internal heating by sensible heat of a highly heated condensable or non-condensable gas; internal firing, supplied by partial combustion of the coal or by partial combustion of a combustable gas used, for example, to fiuidize the coal; hot coke heating, whereby the hot coke is mixed in the carbonizer with the powdered coal or is passed directly into the boiling bed of a carbonization vessel, or any other suitable method may be employed.

The accompanying diagrammatic sketch illustrates one method of operating the process, wherein exceptionally high yields of ethylene can be obtained. Figure 1 is a plan view of apparatus which may be employed in carrying out the process of the invention and Figure 2, a sideelevation, more in detail of the apparatus of Figure l. The coal is passed into a suitable crusher i, such as a ball mill screening unit, wherein it is pulverized, and screened to give a powdered coal of the optimum particle size. From crusher I the coal is dropped into hopper 2 from which it flows by gravity or through a vibrating feeder, into pipe 3 from which it is blown by air from blower 3 through pipe 5 into a cyclone dust separator 6 from which the coal particles drop into the stand pipe 1. In this pipe the coal particles are in a free-flowing state and during operation or" the process the pipe is maintained substantially filled by continuous addition thereto as coal is removed from its base. From the jacketed stand pipe I, which provides a static head similar to a hydraulic head, the coal is fed by means of the vibratory tubular feeder 8, which is jacketed with steam to prevent condensation and maintain the coal particles in a dry state, through aperture 9 into the pipe [0. A stream of low-pressure steam 1.0 to p. s. i. passes through the falling particles from aperture 0 and carries them into pipe l8, wherein they are maintained by the steam in a fluidized (entrained stream) state, that is, the coal and steam are so intimately and thoroughly mixed that the mixture acts substantially as a flowing gas. Care is required to attain this result, the ratios of coal to steam being held between about 0.5 to parts by weight of coal per part of steam. From pipe :0 the fluidized mixture of steam and coal particles is injected into the coking zone or converter H which is cylindrical in shape and has a conical bottom. Into this converter superheated steam is injected at a temperature between 900 and 1500 C., if the coking is to be conducted under high temperature carbonization conditions. The superheated steam is injected tangentially so that it swirls about the periphery of the converter and gradually as it loses heat to the coal particles, spirals into the center of the converter, the coal spirals in the same circular direction but travels from the center of the converter to the; walls.

i'he superheated steam or other heating fluid is introduced into the converter to supply, preferably, the lowest temperature to the uncoked and the highest temperature to the coked coal. It is known that when coal is heated to temperatures between 350 and 400 C., it passes through what may be called a plastic or softened state, in which state it is very sticky and if permitted to do so will stick firmly to most surfaces. As the volatile matter is distilled from the coal particles at temperatures above 400 C., the plastic state is passed and the particles return to the solid non-plastic, non-sticky state as coke. The tangential introduction or" the heating fluid maintains the highest temperature in the converter on its outer walls and the lowest temperature in the center. As the coal particles pass from the center outwardly, their temperature is raised from inlet temperature through the temperatures at which it exists in the plastic state and before the particles impinge on the walls of the converter they are coked while passing through the highest temperature zone of the converter which exists as a film about its vertical walls. Consequently, the coal particles when reaching the outer walls of the converter, are in the form of coke which is non-plastic at the temperatures of coking. The coal particles, accordingly, fall downwardly and with the gas pass out the exit 13 from the converter.

As the gases and coke pass from the converter they are quenched by a spray or" water, through pipe lal, which is injected at a sufiicient rate to lower the temperature of the exit stream to in the neighborhood of 600 C. This is done toprevent decomposition of the ethylene which occurs if it is held too long at temperatures substantially above 600 C. The gases and coke pass into the separating zone l5 from the bottom of which the coke is discharged, to a suitable receptacle and all the gases pass through pipe it into a scrubbing tower ll which may be packed with any suitable material such as Raschig rings and wherein water, tars and water-soluble gases are separated from the other gases present. The produced gases are drawn from the scrubber through pipe 18 and treated for the separation of the ethylene by any suitable process while the water-soluble condensable vapor as eilluent passes from the scrubber through pipe l9. 7

The apparatus such as is illustrated by the accompanying drawing may be employed not only for the coking of coal but other carbonaceous materials such, for example, as peat, lignite, tar oils, shale, and especially such highly volatile coals which cake and swell on heating as bituminous, cannel and like coals.

The effect of contact time on the composition of the gas produced is illustrated in Table I. The data from which this table is constructed are based on runs made with Powellton coal ground to a mesh size between and and injected with steam at a temperature of 1000 C. into a vertically positioned hollow quartz tube having a ratio of length to diameter of approximately 1 to 5.3.

According to the table the maximum ethylene yield occurred with a contact time of 0.33 second, the maximum acetylene yield with a contact time of 0.49 second and the maximum yield of higher olefins at the minimum contact time, namely, 0.10 second. At lower temperatures substantially equivalent results are obtained with somewhat longer contact time.

Other means may be employed than that described in the drawing for preventing the caking of the powdered coal particles on the walls of the vessel. It may be accomplished by introducing the superheated steam or other carrier gas along the outer walls of the converter by injecting the steam through a plurality of jets situated at the top and/or bottom of the converter, they being so adapted and arranged that the steam flows parallel to the walls or" the converter and in close proximity thereto. Any other suitable means of introducing the steam so that it acts as a high temperature barrier to the flow of the coal particles toward the walls may be employed. Internal mixing within the converter may be provided by suitable baiiies or one or more steam jets may be enclosed within the steam barrier for violent agitation of the particles in order to insure rapid and uniform heating. The purpose of the steam barrier against the outer wall is identical with its purpose in the converter illustrated in the drawing, viz. to prevent the partially coked coal while in the plastic, sticky state from coming in direct contact with the walls and thereby building up a coke deposit that would quickly clog the converter and require shut down of the process for cleaning.

The examples illustrate preferred embodiments of the invention in which parts are by weight unless otherwise indicated. Examples 1 to 3, inclusive, illustrate operation of the process in equipment somewhat diiferent from that described by the accompanying drawing, while Examples 4 to 6, inclusive, were conducted in equipment similar to that illustrated by the drawing.

Example 1.Carl2onz'eation of powdered cannel coal in steam by radiant heat A West Virginia cannel coal containing 47% volatile matter was ground to 80-150 mesh and fed downward at a rate of 15.8 parts per hour through a vertical, tubular silica reaction chamber having a ratio of diameter to length of 1 to 5.6. The powdered coke accumulated in the bottom of the vessel while gas was taken off through a side tube near the bottom. The converter was externally heated to a temperature of about 1000 0., and the time of contact of the powdered coal at this temperature approximately 0.5 second. The uncondensed gas obtained contained 5.65% ethylene plus acetylene and 1.05% higher olefins. On this basis the yield of ethylene plus acetylene is 203 lbs. per ton. The powdered coke contained 5 volatile matter.

Example 2. Carbonieati0n of powdered bituminous coal in hydrogen by radiant heat Coal from the Powellton seam of West Virginia was ground and sized to 80-150 mesh and was passed downwardly at a rate of 13 parts per hour through a converter along with 21 parts per hour of hydrogen. The converter consisted of a vertical silica tube having a diameter to length ratio of 1 to 12 and was maintained at a temperature of 900 C. by external heating. The coal and hydrogen were admitted into the converter in downward parallel streams. Coke accumulated in the bottom of the tube while gas was removed through a side tube near the bottom. The exit gases after removal of tar and coke were passed over activated charcoal at Dry Ice temperature. The gas was regenerated from the charcoal by heating and contained 3.35% ethylene, 0.4% higher olefins, 0.3% acetylene, 2.2% carbon monoxide, 13.4% paraffin hydrocarbons with an average molecular weight of about 30; it also contained considerable hydrogen and nitrogen. On this basis the yield of ethylene was lbs. per ton and of higher olefins 14 lbs. per ton. The coke contained 6.4% volatile matter.

Example 3.-C'arb0nieati0n of powdered bituminous coal in steam by radiant heat Powellton seam coal (80-150 mesh) described above, was passed at a rate of 13.4 parts per hour downwardly as a fluidized stream with 188 parts per hour of dry steam at substantially atmospheric pressure into a vertical, tubular silica converter having a diameter to length ratio of 1 to 22. The tube was externally heated to a temperature of 800 C. Upon analysis the gases produced had this composition:

CO2 per cent 0.8 Acetylene do 0.5 Ethylene do 2.4 Higher olefins do 1.0 Oxygen do 0.1 Hydrogen do 8.1 Carbon monoxide do 3.5 Parafiins (carbon N0.=1.2) do 7.0 Nitrogen (fed with coal) do 76.6

Yield per ton:

Ethylene pounds 54 Propylene, etc. do 34 Hydrogen-l-CO cu. ft. 3500 The coke contained 11.9% volatile matter.

Example 4.Carbonieation of powdered bituminous coal in superheated steam Powellton seam coal (size mesh to dust) was suspended in C. steam (1 lb. coal per 1b. of steam) and passed continuously at a rate of 10 lbs. per hour as a fluidized stream into a reactor having a diameter to length of 1 to 2 with a conical bottom and a flat top, the bottom being V again as deep as the diameter of the reactor. In the reactor the powdered coal was diluted, heated and coked by steam which had been preheated to approximately 1020 C. and which was introduced into the converter at a rate of 100 lbs/hour, thereby maintaining a reactor temperature of about 925 C. The gases and solids passed through the reactor with an average contact time of about 0.6 second, after which the mixture leaving the bottom of the reactor was immediately cooled by injection of a small stream of water to about 600 C. At this temperature powdered'coke was separated from the gases in a cyclone separator. The remaining gases were further cooled to about 40 C. to condence the carrier steam. The ethylene content of the product gas corresponded to a yield of 40 lbs. ethylene/ton of coal processed.

Example 5.-Powdered Powellton seam coal similar to that used in Examples 4 and 5 was fed to the converter at a rate of 12 lbs/hr. The steam to coal ratio was 17, the reaction temperature 890 C. and the calculated hold-up time was 0.3 second. The ethylene content of the gas produced corresponded to a Cal-I4 yield of 53 lbs/ton of coal.

In the specification and attached claims the coal and coke used withsa carrier gas acts like a fluid and is saidto be in a fluidized state; That, state exists'when; the particulate solid has. increased its bulk volume byat least, 10% due to the flow of gas through; it. As. the velocityof the gas is increased above this amount up to the velocity that produces a boiling bed, the state is calledan extended bed, andwhen the particles have the appearance of a boiling liquid, the state is that of a boiling bed. Beyond the boiling bed statethe gas and solid move forward as a stream, which condition'is called an entrained stream. For practical utility the entrainedstreamshould contain in..the order of 1 pound or more of coal per IOU-cubic feet of gas.

Iclaim:

In a process for the preparation of unsaturated hych'ocarbonsv by the carbonization of pulverized coal, the; steps which comprise. charging. a zone with a static, head of air and pulverized coal, passing the coal-iromsaid zone by the force of the static head; and by the force of steam into a mixing zone to give a thorough intimate-mixture of from 0.5 to 30 parts by weight of coal per part of steam, introducing the resulting mixture into the center of a cylindrical coking. zone, injecting steam at a temperature between 7.00 and 1500 C. tangentially into the cylindrical coking zone whereby the super-heated steam swirls about the periphery of said cylindrical coking zone and spirals into the center ofsaid .zone and whereby the heat for coking the coal flows from the circumference of the cylinder toward its axis, thereby preventing the coal from stick- 3 ing to the cylinder walls while passing; through the plastic state, removing the product. gases from the coking zone at such a rate that the unsaturated hydrocarbons presentthereinare in the coking zone for from 0.5 to 3- seconds and immediately after discharge of the products from the coking zone quenching them with water to a temperature: below 600. C.. the disposition of the coal-steam mixture and the injection of the high temperature steam into the coking zone being so adapted and arranged that coal'and high temperature steam flow. counter-current, the coal from the center toward the walls of the coking zone, the..steam.from the walls. toward the center of the. coking zone.

AD'ONIRAM J. WELLS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITEDv STATES PATENTS Number Name Date Re. 17,181 McEwen Jan. 1, 1929 1,432,170 Fenton. Oct. 17, 1922 1,484,258 Fenton Feb. 19, 1924 1,858,834 Lucke May 17, 1932 1,950,558 Karrick Mar. 13, 1934 2,337,684 Scheineman 1 Dec. 28, 1943 2,406,810 Day Sept. 3, 1946 2,414,586 Eglofi Jan. 21, 1947 OTHER REFERENCES Fluidizing Processes, Chemical Engineering Progress, vol. 43, No.- 8, page 429, August 1947.

Fluidization of Solid Particles, Chemical Engineering'Progress, vol. 44, No. 33, March 1948, page201.

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