US3152869A - Process for making boron trichloride - Google Patents

Description

Oct. 13, 1964 c. BRATT ETAL 3,152,369

PROCESS FOR MAKING BORON TRICHLORiDE Filed Dec. 23, 1960 z -6OM 6OM COAL soups FEED CARBON BORON TAR RAW PITCH MATERIAL -60 M N Punzea 'V /8-' 8 MIXER 0 v /2 2 FORGE PELLETIZER [BRIQUQ'TER] 20 QUENCH LIQUID TO 22 Z4 24 RECOVERY ECKHOFF at; SLICK ATTORNEYS A MEMBER 0F rm: FIRM preferably from A to 1".

United States Patent PROCESS FOR MAKING BORON TRICHLORIDE Lars C. Bratt, Los Altos, and Loren J. Hov, Richmond,

Calif., and George A. Louis, Phoenix, Ariz., assignors to Stauifer Chemical Company, a corporation of Delaware Filed Dec. 23, 1960, Ser. No. 78,187 7 Claims. (Cl. 23-205) This invention relates to the production of boron trichloride by chlorination of a boron-containing material and a carbonaceous reducing agent in a continuous, moving-bed, countercurrent flow reactor. Examples of suitable boron-containing materials are boric oxide, boric acid, decahydrate or anhydrous borax, or borax minerals such as colemanite, kernite or rasorite or combination of two or more of the foregoing. The carbonaceous reducing agent can consist of any commercially available reactive form of carbon, such as charcoal, petroleum coke, bituminous coal or coke.

The carbonaceous material and the boron-containing material are pulverized and preferably ground to 60 mesh-F200 mesh, although any size range convenient to the following agglomeration step may be used, and then mixed intimately with 5-50%, preferably 25%, of a powdered or liquid binder which contains hydrogen and carbon, preferably coaltar or coaltar pitch, although other binders such as asphalt, starch, molasses, or sugar, independently or in combination, may be used. The homogeneous mixture is then agglomerated in a suitable manner so that a granular feed material, suitable for a moving bed reactor, is obtained. This-agglomeration can be accomplished in several ways. In one method, the powdered mixture containing the carbonaceous material and boron-containing material is mixed with 550%, preferably 1025%, of a suitable powdered or liquid binder as described, and the mixture is then devolatilized at 100700 C. and may be sintered at 500-1000 C. The hard material obtained after devolatilizing and/or sintering is then broken up to suitable granules of desired size which can be -4+ but preferably -1",[%".

i A second method to achieve agglomeration is by mixing the feed material mentioned above with 550%, preferably 10-25%, of a suitable powdered or liquid binder, and then to expose this mixture to high pressure as achieved in commercial briquetting machines, pelleting presses or tabletting machines. The briquettes, pellets or tablets may have a particle size of from A to 4" or, The briquettes, pellets or tablets obtained in this manner are devolatilized at 100- 700 C. for a sufficient length of time, generally on the order of eight hours, to remove substantially all water and volatile material and to produce a coking bond in the briquettes, pellets or tablets, and then may be sintered at a sufiiciently high temperature of 500-1000 C. for a sufficient length of time, generally on the order of four 1 in the initial mix be at least 1.75 times stoichiometric as required to yield CO from the reaction of said carbonaceous material and the boron oxide material being treated. Whenever any of the boron-containing materials listed 3,152,869 Patented Get. 13, 1964- "ice above are utilized in a chlorination process requiring a reaction temperature of at least 500 C., a fluid is formed in the reaction zone which will cause agglomeration of the briquettes, if present in excess. Also, a residual coked carbon bonding is obtained which is insuflicient to maintain the discrete briquettes and such briquettes decrepitate, thus resulting in a plugging of the moving bed. Thus, the aforementioned ratio, and preferably a ratio of carbon to boron-containing material of 2:1 based on the stoichiometric requirements to produce CO, must be observed.

The fired briquettes, pellets or tablets are then charged continuously or in slugs to the top of a vertical shaft, moving bed reactor. The briquettes, pellets or tablets can be preheated, preferably to the reaction temperature, before being charged to the reactor to achieve maximum through-put and to reduce the need for heating in the reactor proper. The reactor residue is discharged continuously or in slugs from the bottom of the reactor.

Gaseous chlorine is charged continuously to the reactor through a nozzle connected to the bottom of the vertical shaft reactor. The rate of addition of chlorine should be such as to permit maximum conversion of boron raw material to boron trichloride. Excess chlorine has been found to increase the rate of the reaction and to increase boron efiiciency in addition to reducing the formation of a by-product of the reaction,

while effecting only a small increase in the by-product phosgene formation. The chlorine can be introduced through the spent charge exiting the reactor proper to effect preheating of the chlorine before entering the reaction zone and/or it can be externally preheated. Both modes of chlorine preheating result in increasing reactor capacity to the extent that the temperature of the chlorine entering the reaction zone approaches the reaction zone temperature.

The reaction zone is maintained at a temperature of 5001400 C., preferably 700800 C. When boron raw materials are used which have an endothermic reaction with chlorine in reactions producing boron trichloride, it is obvious that heat must be supplied to the system. This can be done by a suitable method such as electric resistance heating or by the use of an auxiliary compatible exothermic reaction. Such a reaction can be caused by adding oxygen to the chlorine entering the reactor. or by incorporating boron carbide or silicon carbide in the solid feed mixture charged to. the reactor or by adding an excess of commercial charcoal which contains impurities which have an exothermic reaction with chlorine.

If the exit gases from the reactor should contain an objectionable amount of phosgene, it can be substantially reduced by quenching the gases quickly as they emerge from the hot zone of the reactor. This quenching can easily be accomplished by properly injecting a spray of liquid boron trichlOride or other inert non-aqueous liquids such as titanium tetrachloride or vapors into the hot gas immediately emerging from the reactor.

The figure of the drawing illustrates a suitable apparatus for carrying out the invention. Referring to the drawing by reference characters, there is shown a source of finely divided carbon 2, a source of finely divided boron raw material 4, and a source of binder 6, which is indicated in the drawing as coal tar pitch. These materials are brought together in mixer 8 and then passed to either a pelletizer 10 or a briquetter 12. The pelletized or briquetted material is then devolatilized at 14 and sintered at 16. If the material issuing from the sintering device 16 is not of the desired particle size, it is then crushed or ground and classified to the desired size by means not illustrated.

The material is then passed to the gas lock 18 and to the feed drum 20. The feed system is provided with a nitrogen purge in 18 and 20, thereby excluding air and preventing loss of reactant gases. The material is then passed through the screw feeder 22, which is equipped with heater 24. From the screw feeder 22, the material is passed into the reactor 26 which is a tube of an inert material, such as carbon or graphite, capable of withstanding a high temperature under the reaction conditions. Gaseous reaction products are withdrawn at 28 where a quench nozzle 29 may be inserted as heretofore described for rapid cooling of effluent. The reactor 26 is surrounded by an insulating jacket 30 in which are embedded resistance heaters 32. Chlorine is introduced through a rotometer 34 and preheater 36 to the bottom of the column at 38. Spent solids are withdrawn from the bottom of the column through the screw conveyor 40 and into the ash receivers-42. The latter are kept under a nitrogen purge and are removed alternately to prevent air from entering the system.

The following non-limiting examples illustrate preferred methods of practicing the invention:

Example 1.--Twenty-five pounds of anhydrous borax powder was mixed with twenty pounds powdered coal tar pitch and fifty-five pounds powdered charcoal. Twelve pounds of petroleum oil was blended into this mixture and the homogeneous material was pelleted through a pelleting press using a /s" to /2" choke die resulting in pellets Mz" thick and 1" long. The pellets were devolatilized, dehydrated and cokedby effectively raising their temperature-from 100 to 400 C. over an eight hour period and then sintered by increasing the temperature to 750 C. for four hours. The devolatilized and sintered pellets were then transferred to a storage hopper from which they were charged slug-wise at a rate of 33 pounds per hour through a preheater at 500600 C. into the top of a moving bed reactor maintaining the level of the top of the charge in the reactor constant within six inches. The reactor tube, made of carbon and graphite tubes, was six inches inside diameter, seven feet long, and was maintained at its surface at 750 C. by means of electric resistance heaters. Chlorine vapor was fed continuously at a rate of 25 pounds per hour to the bottom of the reactor. The average retention time of the moving pellets in the heated chlorination zone was 90 minutes. The boron trichloride-containing olf gas was Withdrawn continuously from the top of the reactor with an approximate weight percent composition of Percent BCl 42 HCl 19 CO 11 N C1 7 CO 6 COCl 1 Smoke (B O /5BCl 4 The boron trichloride was produced at a rate of 16 pounds per hour. Analysis of the spent pellets exiting the reactor showed 88% of the input boron reacted.

Example 2.Fifty pounds of boric oxide powder was mixed with one hundred fifty pounds powdered charcoal and forty pounds powdered coal tar pitch. The homogeneous mixture was preheated to 200 F. and briquetted by means f a Belgian roll briquette press to pillow shaped briquettes approximately long and /2" thick. The briquettes were handled in the same manner as the pellets in Example 1 and charged slug-wise at the rate of 54 pounds per hour to the moving bed reactor which reacted out.

was maintained at its surface at 700 C. Chlorine vapor was fed continuously at a rate of 29 pounds per hour to the bottom of the reactor. The average retention time of the moving briquettes in the heated chlorination zone was 39 minutes. The boron trichloride-containing olf gas was withdrawn continuously from the top of the reactor with an approximate weight percent composition of Percent BCI 36 HCl 42 N 9 CO 6 CO 3 Smoke (B2O31/5 4 C1 Nil COC1 Nil effectively raising their temperature to 700 C. over an eight hour period and charged slug-wise at the rate of 26 pounds per hour to the moving bed reactor which was maintained at its surface at 750 C. Chlorine vapor was fed continuously at a rate of 27 pounds per hour to the bottom of the reactor. The average retention time of the moving pellets in the heated chlorination zone was 118 minutes. The boron trichloride-containing off gas was withdrawn continuously from the top of the reactor with an approximate weight percent composition of Percent BCl 46 HCl 18 N 8 C1 6 CO 5 COCl 1 Smoke (B O /5BCl 4 The boron trichloride was produced at a rate of 16 pounds per hour. Analysis of the spent pellets exiting the reactor showed 93% of the input boron reacted;

Example 4.Eighty-five pounds of anhydrous borax powder was mixed with twenty-nine pounds of powdered coal tar pitch and fifty-six pounds of powdered charcoal. Nineteen and a half pounds of petroleum oil was blended into this mixture and the homogeneous material was pelleted through a pelleting press using a hole diameter straight run die resulting in pellets /8 thick and from A1" to 1" long. These pellets were devolatilized, dehydrated and coked by elfectively raising their temperature to 700 C. overan eight hour period. They were then charged by frequent intermittent screw feeding to essentially maintain a constant bed level at a rate of 0.62 cubic feet per hour to a vertical moving bed reactor. The reactor tube of carbon and graphite was six inches in diameter with a five foot long heated section maintained at its surface at 750 C. Chlorine vapor was fed continuously at a rate of fifty-four pounds per hour to the bottom of the reactor and boron trichloride-containing product vapors were continuously withdrawn. Analysis of the pellets fed to the reactor showed 58% borax and analysis of the spent charge showed 93.6% of this borax The carbon content of these pellets was 1.75 times the amount required by the stoichiometry of the reaction equation:

surgeon This application is a continuation-in-part of application Serial No. 628,304, filed December 14, 1956, now abandoned.

We claim:

1. In a process for making boron trichloride wherein a mixture of a boron-oxide containing material and a solid carbonaceous reducing agent consisting essentially of carbon is devolatilized and dehydrated and the mixture so formed is treated in a vertical moving bed reaction zone with chlorine at a temperature of between about 500 and 1400 C., the improvements comprising: adjusting the level of solid carbonaceous reducing agent relative to boron-oxide containing materials in the initial mixture to at least about 1.75 times the stoichiometric requirements to produce entirely CO from said carbonaceous reducing agent and said boron oxide containing material; adding a coke-forming binder to the said mixture at the time of formation thereof; forming said mixture into agglomerates having a dimensional range between about ,1 and about 4" and dehydrating and devolatizing by heating the said mixture at a temperature of between about 100 and 700 C. for a time suflicient to remove substantially all water and other volatile material and to produce a coking bond therein, said forming of agglomerates and heating preceding contacting said mixture with chlorine; charging said agglomerates so formed into the top of a vertical reaction zone and passing said agglomerates downwardly while passing chlorine into the bottom of said reaction zone and allowing said chlorine to pass upwardly therethrough; and recovering boron trichloride from the top of said reaction zone.

2. The process of claim 1 wherein said agglomerates are formed by heating the mixture at an elevated temperature to form a coking bond and breaking up the coked mass so formed.

3. The process of claim 1 wherein said agglomerates are obtained by applying high pressure to the mixture obtained prior to devolatilization and said agglomerates are thereafter dehydrated, devolatilized and coked.

4. The process of claim 1 wherein said binder is present in the quantity of between about 5 and by weight.

5. The process of claim 1 wherein said binder is present in the quantity of between about 10 and 25% by weight.

6. The process of claim 1 wherein the binder is coal tar pitch.

7. The process of claim 1 wherein the binder is coal tar.

References Cited in the file of this patent UNITED STATES PATENTS 2,097,482 Weber Nov. 2, 1937 2,378,675 Agnew et al June 19, 1945 2,876,076 Montgomery et a1 Mar. 3, 1959

Claims (1)

1. IN A PROCESS FOR MAKING BORON TRICHLIRIDE WHEREIN A MIXTURE OF A BORON-OXIDE CONTAINING MATERIAL AND A SOLID CARBONACEOUS REDUCING AGENT CONSISTING ESSENTIALLY OF CABON IS DEVOLATILIZED AND DEHYDRATED AND THE MIXTURE SO FORMED IS TREATED IN A VERTICAL MOVING BED REACTIN ZONE WITH CHLORINE AT A TEMPERATURE OF BETWEEN ABOUT 500* AND 1400*C., THE IMPROVEMENT COMPRISING: ADJUSTING THE LEVEL OF SOLID CARBONACEOUS REDUCING AGENT RELATIVE TO BORON-OXIDE CONTAINING MATERIALS IN THE INTIAL MIXTURE TO AT LEAST ABOUT 1.75 TIMES THE STOICHIOMETRIC REQUIREMENTS TO PRODUCE ENTRIRELY CO FROM SAID CARBONACEOUS REDUCING AGENT AND SAID BORON OXIDE CONTAINING MATERIAL; ADDING A COKE-FORMING BINDER TO THE SAID MIXTURE AT THE TIME OF FORMATION THEREOF; FORMING SAID MIXTURE INTO AGGLOMERATES HAVING A DIMENSIONAL RANGE BETWEEN ABOUT 1/16" AND ABOUT 4" AND DEHYDRATING AND DEVOLATIZING BY HEAT THE SAID MIXTURE AT A TEMPERATURE OF BETWEEN AB OUT 100* AND

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