US2789037A - Process for the preparation of carbon disulfide - Google Patents

Description

April 16, 1957 c. N. KIMBERLIN, JR., Erm. 2,789,037

PROCESS FOR THE PREPARATION OF CARBON DISULFIDE Filed Dec. A10. 1954 il States Patent PROCESS FOR THE PREPARATION OF CARBON DSULFIDE Charles Newton Kimberlin, Jr., Baton Rouge, and Ralph Burgess Mason, Denham Springs, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application December 10, 1954, Serial No. 474,552

5 Claims. (Cl. 23-206) This invention relates to an improved process for the preparation of carbon disulde. More particularly it relates to the pretreatment with an oxygen-containing gas of petroleum coke, especially fluid coke, so that it can be better subsequently reacted With sulfur vapor for the production of carbon disulfide.

This application is a continuation-in-part of application Serial No. 431,412, iiled May 21, 1954 which has issued as Patent No. 2,721,169, October 18, 1955.

The reaction between carbon and sulfur vapors to produce carbon disulfide is well known. Hardwood charcoal constitutes the primary source of the carbon. lncreased demand for the carbon disulfide as a raw material in the manufacture of viscose rayon makes the tapping of other sources of carbon desirable.

Petroleum coke produced from heavy residual stocks typically have a low surface area. This impedes the rapid and satisfactory production of carbon disulfide by reaction of the coke with the sulfur. It is therefore advantageous to employ carbons having high reactivity for carbon disulide manufacture since with the less reactive forms of carbon, such as petroleum coke, it is necessary to conduct the reaction with sulfur at higher temperatures where the corrosive action of the sulfur vapor becomes a serious problem. For practical purposes carbons having a surface area of about 50 m.2/g. or higher may be employed for the manufacture of carbon disulfide; however, even higher surface areas, such as 100 m.2/g. or more, are desirable.

Petroleum coke hasrbeen obtained largely from coking processes such as delayed coking which provides particles of relatively large diameter and densities.

There has recently been developed another source of petroleum coke known as the uid coking process for the production of uid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel usually but not necessarily separate. 7Eluid beds are employed but transfer line systems can be used also. In a typical operation the heavy oil to be processed is injected into the reaction vessel containing a dense turbulent lluidized bed of hot inert solid particles, preferably coke particles.l Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. Staged reactors can be employed. In the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking Vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coki'ng vessel. The coke produced in the process remains inthe bed coated. ou the solid. particles.

tripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the heater or burner vessel. A

stream of coke is transferred from the reactor to the burner vessel employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Suicient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% to 10% of coke, based on the feed, isl burned for this purpose. The unburned portion of the coke represents the net coke formed in the process and is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and vacuum crude bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically such feeds can have an initial boiling point of about 700 F. or higher, an A. P. l. gravity of about 0 to 20, and a Conradson carbon residue content of about 5 to 4() wt. percent. (As to Conradson carbon residue see A. S. T. M. test D-l80452.)

lt is preferred to operate with solids having a particle size ranging between 100 and 10G() microns in diameter with a preferred average particle size range between 150 and 400 microns. Preferably not more than 5% has a particle size below about microns, sinceV small pap ticles tend to agglomerate or are swept out of the system with the gases.

The method of fluid solids circulation described above is well known in the prior art. Solid-s handling technique is described broadly in Packie Patent 2,589,124, issued March 11, 1952.

The uid colte product is laminar in structure and may comprise some 30 to 100 supeiposed layers of coke. The size `distribution is such that a predominant portion, i. e., about weight percent has a diameter smaller than. 400 microns with a range of about 75 to 850 microns.

Fluid coking has its greatest utility in upgrading the quality yof low grade vacuum residua and pitches from highly asphaltic and sour crudes. Such residua frequently contain high concentrations of sulfur of 3% or more and the coke product produced from these high sulfur feeds are also high in sulfur content. In general the sulfur coutent of the coke product from the iluid ooking process may be in the range of l to 2 times the sulfur content of the residuum feed from which it is produced. The sulfur content of coke from sour residua may thus range from 5% to 9% sulfur or more, or substantially more than coke from non-petroleum sourcesV and most non-Huid or delayed petroleum coke.

This invention makes it possible to utilize petroleum coke and particularly fluid coke in the manufacture of carbon disulde. The process comprises subjecting the coke particles, preferably in the form of a dense turbulent uidized bed, to a low temperature oxidation pretreatment with an oxygen-containing gas. The coke which has been heated to some extent by the oxidation can then be utilized directly in the subsequent steps for the manufacture of the carbon disulfide.

The pretreatment with the oxygen-containing gas is conducted at a temperature of 690 to 1G00 F., preferably 650 to 850 E. This low temperature .oxidation treatment is preferably carried out while the coke particles are in the form of a dense turbulent fluidized hed. While it may be possible to effect the desired result Vof the low temperature 'oxidation by treatment of a fixed Ybed or moving fixed bed of coke with an oxygen-containing gas, the problem of removing the heat of .reaction from a fixed bed, except in the case of very small xed beds, makes Vthe control. of4 temperature very diicult in this type of operation. In contrast to a fixed bem-the tera-y perature of oxidation is very easily controlled when tration. and pressures.

oxidizing coke in a uid bed by treatment with an oxygencontaining gas. The temperature mayl be controlled by means of coils immersed in the fiuid bed. lt is 1ndeed surprising that these low temperature levels are necessary andthat higher temperatures produce worse results as the reverse would normally be expected. The oxygen-containing gas can be atmospheric air or air enriched with oxygen at atmospheric or superatmospheric pressures. The time of the oxygen treatment can range broadly within the range of minutes to 50 hours as will depend on the temperature and the oxygen concen- When conducting the pre-oxidaltion at the higher temperatures of about 800 to l000 F. within the operable range, it may be preferred .to employ air delicient in oxygen such as air diluted with nitrogen, ilue gas, or the like. At the lower end oxygen enriched air can be used. lf desired a part ofthe exit gases from the oxidation may be recycled to the oxidation'zone. The best control feature within these ranges is the yield loss of the coke subjected to the oxidation. The conditions are controlled within the preceding ranges so that a maximum yield loss of 2O weight percent, preferably l0 weight percent, or conversely a minimum yield of 80, preferably 90 weight percent, is obtained. For certain special applications of the low temperature oxidized coke it may be desirable to oxidize to a greater extent, for example, to a yield of 50% to 60%; however, for most cases yields below about 80% are uneconomical. The low temperature oxidation is a non-catalytic reaction and it is not necessary to add a catalyst to the system.

The coke is then utilized in the preparation of carbon disullde by means known in the art. Carbon disulde is produced by reacting the pretreated coke and sulfur in the presence of heat furnished by electrothermal or retort methods. These in themselves are no part of this invention but are detailed below for completeness.

In the electric furnace process the coke is charged into the top of a vertical shaft located above the hearth in a specially constructed resistance-type furnace. Around this circular hearth are located four carbon electrodes, placed horizontally and symmetrically. The electrodes, each 4 ft. long and 20 in. in diameter, are arranged so that they are about 1 ft. apart in the middle of the furnace. Between the ends of the electrodes are pieces of coke, which act as resistors. Sulfur is charged through channels in the walls of the hearth and in the shaft located near the furnace base. The furnace, which may vary in size from 240 to 360 kw. at 60 volts and 4,000 to 6,000 amperes, is fed with twophase alternating current, which generally passes between opposite electrodes.

At operating temperature 'of the furnace, about 1450 to l850 F., the sulfur vaporizes and reacts with the coke to form carbon disulfide and small amounts of byproducts. The gaseous products pass up through the shaft to condensers, in which the carbon disulfide is liquefied. A high temperature is required to obtain a suciently fast reaction rate; it is controlled by regulating the voltage and rate of raw-material feed. i In the retort process, the reaction takes place in di-V rect-tired retorts of cast iron or refractory rebrick. As in the electric-furnace process, previously pretreated coke is charged from the top, sulfur at the bottom, and, at a temperature of 1400 to l850 F. in the absence of air, carbon disulfide is formed. Usumly natural gas or producer gas is used to dre the retorts, but any fuel may be employed. Y

I'he carbon disuliide gases formed in either type furnace pass through a side outlet in the shaft into coolers or Water condensers. The uncondensed gases are fed into absorbers where countercurrently owing mineral oil'removes the residual carbon disulfide; the washed gases, mostly hydrogen sulfide, pass into storage tanks.

The absorbed carbon disulfide is freed from the mineral oil iby' distillation; the oil is returned to the absorbers for re-use, and the disulfide is combined with the liqueed carbon disulde from the condensers. It is then run into continuous-distillation units. Here it may rst be distilled in a hot water still; the liquid crude 'disulfide is admitted by an aluminum spray nozzle. The disulfide volatilizes as it falls on the hot (175 F.) water. Unreacted sulfur separates and falls to the bottom of the still. From here the gaseous carbon disulfide is cooled, the water is removed by decantation, and the cooled carbon disulfide is passed into a fractionating column where residual hydrogen sulfide is removed. The hydrogen sulde goes to thestorage tank, from where it may be passed into a packed tower to be burned under reducing conditions, in the presence of a catalyst such as bauxite, to recover sulfur.

The fractionated carbon disulfide may be washed with 5% caustic soda in a packed (porcelain rings) tower and condensed to give a 99.99 percent product.

Alternatively the uid solids technique can be used for the reaction. -Thus, the heat can be supplied by combustion of a portion of the iiuid coke and the reaction is carried out by contacting the finely divided hot coke with a stream of sulfur under conditions where the carbon is tluidized in the sulfur vapor in the reaction zone, e. g. see U. S. Patent 2,480,639 of August 30, 1949.

Because lof its particle size and easily uidizable nature coke produced in the fluid coking process and pretreated by low temperature oxidation according to the present invention is particularly adapted to the production of carbon disullde by the fluid solids process.

The theoretical quantities of carbon and sulfur utilized are in accordance with the equation: C|2S CS2. For example, to prepare one ton of carbon disulfide about 350 lbs. of carbon and 1875 lbs. of sulfur are required taking into account losses and side reactions, with from 800 to'l,000 kw.hr. or equivalent fuel. Since the petroleum coke contains some of the sulfur required for the reaction, the amount of extraneous sulfur required is consequently reduced. For example, when employing a petroleum coke containing about 7 wt. percent sulfur produced by coking a residuum from sour crudes about 375 lbs. of coke and 1850 lbs. of sulfur may be required to produce one ton of carbon disulde, when taking into account losses and side reactions.

This invention will be better understood by reference to the following example and oW diagram shown in the drawing.

EXAMPLE l The drawing shows a preferred form of apparatus suitable for the pretreatment of coke by low temperature oxidation and the conversion of the low temperature oxidized coke'to carbon disulfide by reaction with sulfur ernploying the uid solids technique. Fluid coke produced by the fluid coking of the residuum from the vacuum distillation of Hawkins crude oil is withdrawn from the coker burner (not shown) by line 1 into vessel 3 which comprises a low temperature oxidation or pre-treatment zone. The uid coke is withdrawn from the coker burner by line 1 at a temperature of 1100 F.; it has a sulfur content of 7 wt. percent, an average particle size of about 350 microns, and a surface area of 5 m/ g. In vessel 3 the coke forms a Huid bed 5 which is uidized and oxidized by an upward ow of'air introduced by line 7. The velocity of air in vessel 3 is l ft./ sec. The temperature of liuid bed 5 is maintained at 700 F. by cooling coil 9 in which steam generated. The fluid coke remains in vessel 3 for an average residence time of 5 hours during which 7% of its weight is removed by oxidation and its surface area is increased to m.2/ g. The total amount of air entering'vessel 3 by line 7 is about 42,000 cubic feet for eachton of coke entering vessel 3 by line 1. After passage through bed 5 the air, which has had its oxygen only partially consumed, is passed Vby line 11- into heater vessel 29 where it supports the combustion of coke y The temperature in the carbon disulfide reactor can be maintained by circulation of an inert solids heat carrier such as shot. The latter is heated preferably in a trans'- fer line burner by combustion of extraneous fuel'such as gas or fuel oil.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made with# out departing from the spirit of the invention.

What is claimed is:

l. In a process for the production of carbon disuliide I by the reaction between uid coke product particles and sulfur vapor under reaction conditions at a temperature in the range of 140 to l840 F., said particles having been produced by the steps of contacting a heavy petroleum oil, ccking charge stock at a coking temperature with a uidized body of coke particles in a reaction zone, wherein `the oil is converted to product vapors and carbonaceous solids are continuous deposited on the coke.

particles; removing product vapors from the coking zone; heating a portion of the coke particles removed from the coking zone with an oxygen containing gas in a heating zone to increase the temperature of said particles to one in the range of 1050 to l600 F.; returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing product coke particles, the

improvement which comprises pretreating the already "comprises high sulfur uid coke particles.

3. The process of claim 2 in which the pretreatment with an oxygen-containing gas is conducted while the huid coke particles are maintained in the form of a dense,

turbulent, iluidized bed.

4. The process of claim 3 in which the pretreatment is conducted at a temperature in the range of 650 to 850 F. and the pretreated coke has a minimum surface area of 100 nmz/g.

5. The process of claim 3 in which-a portion of the coke particles is withdrawn from the reaction step with sulfur vapor, heated to a temperature between l500 and 2200 F. and returned to the sulfur vapor reaction stepv to supply heat thereto.

References Cited in the le of this patent UNITED STATES PATENTS Ferguson June 22, 1948 Belchetz Nov. 8, 1949

Claims (1)

1. IN A PROCESS FOR THE PRODUCTION OF CARBON DISULFIDE BY REACTION BETWEEN FLUID COKE PRODUCT PARTICLES AND SULFUR VAPOR UNDER REACTION CONDITIONS AT A TEMPERATURE IN THE RANGE OF 1400* TO 1840* F., SAID PARTICLES AND BEEN PRODUCED BY THE STEPS OF CONTACTING A HEAVY PETROLEUM OIL, COKING CHARGE STOCK AT A COLING TEMPERATURE WITH A FLUIDIZED BODY OF COKE PARTICLES IN A REACTION ZONE, WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS SOLIDS ARE CONTINUOUS DEPOSITED ON THE COKE PARTICLES; REMOVING PRODUCT VAPORS FROM THE COLING ZONE; HEATING A PORTION OF THE COKE PARTICLES REMOVED FROM THE COKING ZONE WITH AN OXYGEN CONTAINING GAS IN A HEATING ZONE TO INCREASE THE TEMPERATURE OF SAID PARTICLES TO ONE IN THE RANGE OF 1050* TO 1600* F.; RETURNING A PORTION OF THE HEATED COKE PARTICLES FROM THE HEATING ZONE TO THE COLING ZONE AND WITHDRAWING PRODUCT COKE PARTICLES, THE IMPROVEMENT WHICH COMPRISES PRETREATING THE ALREADY

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