CA1131882A - Method for easily removing zinc from carbon black contaminated with zinc - Google Patents
Method for easily removing zinc from carbon black contaminated with zincInfo
- Publication number
- CA1131882A CA1131882A CA364,920A CA364920A CA1131882A CA 1131882 A CA1131882 A CA 1131882A CA 364920 A CA364920 A CA 364920A CA 1131882 A CA1131882 A CA 1131882A
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- carbon black
- zinc
- weight
- chlorine
- chloride
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Abstract
A METHOD FOR EASILY REMOVING ZINC FROM
CARBON BLACK CONTAMINATED WITH ZINC
Abstract of the Disclosure:
The present invention relates to a method for removing zinc from solid carbon black, preferrably obtained from the pyrolysis of rubber, said carbon black containing at least 3%, by weight, of zinc, calculated as ZnO, said method including the steps of contacting the carbon black at a temperature of at least 732° C. with a gas selected from chlorine and hydrogen chloride to form gaseous zinc chloride from the zinc contained in said carbon black, and separating the gaseous zinc chloride from the solid carbon black.
CARBON BLACK CONTAMINATED WITH ZINC
Abstract of the Disclosure:
The present invention relates to a method for removing zinc from solid carbon black, preferrably obtained from the pyrolysis of rubber, said carbon black containing at least 3%, by weight, of zinc, calculated as ZnO, said method including the steps of contacting the carbon black at a temperature of at least 732° C. with a gas selected from chlorine and hydrogen chloride to form gaseous zinc chloride from the zinc contained in said carbon black, and separating the gaseous zinc chloride from the solid carbon black.
Description
~3~
Back~round of_the Invention;
As is known in the art, carhon black is a ver~ useful com~odity and IS obtained from many resources. Amony the valu-able uses o~ carbon black i5 in the production of rubber tires.
~s a matter of fact, outside of rubber, the major portion of rubber tires is carbon black, and it would be very desirable if such car~on black contained in rubber tires could be reused again. The recycling of carbon black and obtaining useful pro-ducts from rubber contained in tires serves a two~fold purpose:
first, it would conserve our valuable resources and, second, it would ease the problem of what -to do with discarded rubber tires.
For example, at least two hundred million rubber tires are dis-carded in the Uni-ted States every year. And, although such tires make up a relatively small fraction of the solid waste, tires are very difficult to dispose of.
When rubber tires are burned, they give off large quan-tities of unburned hydrocarbons which are highly visible and noxious. Moreover, the problem of disposing of scrap rubber tires is not solved by using the tires as land fill because tires are resistant to natural decomposition and eventually emerge at 20 the surface of the land fill where their appearance is objection-; able.
Another approach to the pro~lem of what to aO with discarded rubber containing carbon b~ack, for example, rubber tires, is to pyrolyze the rubber tires to obtain valuable hydro~
carbons therefrom. However, after the hydrocarbons are removed, a great deal of solid material remains, said solid material (usually called char) bein~ composed primarily of carbon black and inorganic material primarily composed of zinc and sulfur.
~2--~3 ~8~
Carbon black cannot be success~ully reused to make, for example, ruhher tires, unless such inarg~nic Inaterial is removed from the carbon hlack. Moreover, since the primary metal included within the inorganic ma-terial is zinc, normally as zinc oxide, it is desirable to remove -the zinc in order to render the solid char reusable in pxoducing rubber tires, and, at: the same time, re-covering the zinc in order to be able to reuse this valuable metal.
~ummary o~ the ~nvention:
_~_ ___ The present invention relates to a me-thod or process of removing zinc from carbon black (for example, char residue re-maining after pyrolyzing of scrap rubber) containing upwards of 3~ zinc, calculated as zinc oxide. Additionally, the present process provides for the recovery and reuse of the zinc as well as allowing the char, composed primarily of carbon black, to be reused, for example, in the production oE rubber tires or any other product using carbon black. In essence, the present in vention allows for the recycling of solid carbon black which is contaminated with zinc oxide and perhaps other inorganic ~ 2Q -materials~sùch as sulfur, calcium oxide, and very minox-arnounts of other metal.
It is therefore the primary object of the present inven-tion to disclose and provide a process for removing substantially all of the zinc or zinc oxide contained in carbon black in order to be a~le to recycle the carbon black and to recover the zinc contained in said carbon black.
~ further object of the present invention is to disclose ~ ~3~
and provide an economical process for ~ecycllng carhon black and retainlng zinc oxide h~r slmple and econo~lcal process wherein the car~on ~lack is merely con-tacted with a gas such as chlorine at a temperature of ~rom ahout 732C to 1000C or 1200C and separating -the volatile zlnc chlorlde formed thereby from the solid carbon black.
Other objec-ts of the present in~ention will be apparent to those skilled in the art from the following detalled descrip tion wherein all parts and percentages are by weight, unless lQ expressly stated otherwise, and all temperatures are in degrees centigrade unless expressly stated otherwise.
Description of the Preferred Embodimen'ts In the preferred exemplary embodiments, the present in-vention will be illustrated with char produced from scarp rubber, said char belng composed of primarily carbon black (e.g. from 60% to 70%~ by weight, of carbon black, to as high as 85~ to 90 carbon black). The remainder of the char is usually designated as ash and the predominant portion of ~he ash is zinc, as zinc oxide, and sulfur. That is to say, of the ash, at least 50%
thereof will be zinc, as zinc oxide, and sulfur. In general, the zinc oxide will comprise at least 3% of the total weight of the char and the sulfur will normally comprise at least 1% to 1 2% of the char. In the preferred exemplary embodiments, the char used is obtained by pyrolyzing scrap rubber by contacting the rubber with heat carrying solids in a rotating retort.~
During the pyrolysis step, because of the rotation of the retort, ~, ' the heat carrylng sol~ds ('which are preferrably ceramic~ are mixed with the rubber so that not only is the heat transferred ~' ,~ `
from the hea-t carr~in~ sol.ids to -the rub.ber hu-t the rubber is ground so tha-t the sol:id remaining a-ter the pyrolysis and grinding step is of very fine particle size. ~ecause of this very fine particle size, there is a problern with "dusting".
Therefore, it is normal, in order -to prevellt "dusting", to make pellets of the finely divided particles of carbon hlack. Sur-prisingly, the present invention can remove, ~or example, the zinc oxide, from such.carbon black pellets and not adversely af-fect the physical integrity of the pelletized carbon black.
lQ That is, after pelletized carbon black is subjected to the in-stant process, the pelletized carbon black does not lose its shape or form; however, it should be noted that the pelletized carbon black may lose some of its strength bu-t not in such an amount that dusting is a problem.
The objects o-f the present invention are accomplished by contacting carbon black, contaminated with zinc oxide and sulfur, wherein the carbon black is either in finely divided form or in pelletiæed form, ~ith non-aqueous chlorine gas or hydrogen chloride gas at a temperature of at least ahout 732C, and pref-errably, 750C to about 1000C or 1200C. Surprisingly, using either chlorine gas or hydrogen chloride gas at such tempera-tures removes at least 18% of the zinc contaminating the carbon black and in actual practice, over 99%, by weight, of the zinc was removed utilizing the process of the present invention. Sub-stantially all of the zinc removed can be recovered and recycled.
The amount of chlorine gas or hydrogen chloride gas used Ln purifying the carbon black contaminated with zinc or zinc oxide can vary widely, but since one of the objects oE the ' 3~
present invention is to :insure that all, or suhstantially all, of the zi:nc o~ide or ZInC iS removed, it is therefore desi.rable if at least a stochiome-tric a~ount o:E chlorine gas or hydrogen chloride gas is allowed to contact the carbon black. It is pre~erred if a stochiometric excess of chlorille contacts the carbon black. The actual amount oE chlorine which should con-tact the carbon ~lack can he determined by testing the vapo~s given off with potass~um iodide which will indicate when free chlorine is present in the volatile gas. If such occurs, then lQ this indicates that substantially all of the zinc or zinc oxide has ~een removed as a volatile zinc chloride salt.
The reaction between zinc oxide and chlorine, in the presence of car~on, is as fo].lows: 3ZnO ~ 3C12 ~ 2C --~3ZnC1 CO ~ CO2. Thus, i-t can be seen that for one mole of zinc oxide present in the ash, at least one mole of chlorine shoul~ be used.
Stated differently, for every one hundred parts, by weight, of zinc oxide, at least about ninety parts, by weight, of chlorine should be used~ However, since the zinc oxide is present in I relatively small amounts, some of the chlorine will not react 2a with the zinc oxide, at least equal amounts of chlorine should be used based on the weight of the zinc oxide present.
We have found that, in general, for every one hundred parts of carbon black containing at least 3%, by weight, o-E
zinc, calculated as zinc oxid.e, there should be used at least twenty parts, by weight, of chlorine, and preferrably, at least thirty or forty parts by weight, of chlorine. There is no ma~i-mum amount of chlorine that should be used since, on~e the re-action is complete, it makes no difference if more chlorine is ~6--~3~
added except, o~ course, it is uneconomical. However, from a practical standpoint, we have ~ound that, in ~eneral, no more than one hundred parts need be used for each one hunclred parts, by ~eight, of car~on ~lack containing the zinc. The reason that S more -than a stochtometric excess of chlorine is desirable is hecause a certain amount is retained in the! carbon black and a certain amou.nt reacts with other oxides present in the carbon black reacting with khe zinc, and if present, the sulfurO The amounts indicated above also insure that subs-tantially all oE the 10. zinc oxide and sulfur, if present, is removed.
It should be noted that gaseous, non-aqueous hydrogen ; chloride works equally as well as chlorine in the present inven-tion. Moreover, the amount of hydrogen chloride necessary to be used in the present invention is about the same as the amount of chlorine gas since the molecular wéight of hydrogen chloride is about half as great as chlorine gas and because hydrogen chloride provides half as much chlorine as gaseous chlorine does. Thus, from a practical standpoint, at least about twenty parts, by weight of hydrogen chloride should be used for each one hundred parts,-by weight oE carbon black containing zinc oxide, and sometimes s~lfur. It is preferrable if at least thirty parts, by weight, or forty parts, by weight, of hydrogen chloride is used for each.one hundred parts, by weight, of carbon black since this insures that substantially all of the zinc and sulfur, : 25 if present, is remo~ed from the carbon black. Also, as pointed out above with respect to the chlorine gas, we have ound that in general, the maximum amount of hydrogen chloride generally necessary is one hundred parts, by weight of chlorine for each :
, z one hundred parts of carhon b.l~ck.
A~ h~s been noted, -the temperature ~t which the non-aqueous ~aseous chlorine, or n~n-a~ueous, gaseous hydrogen chloride contacts -the carhon black should be at least 732C.
~rom purely t~eoretical consideration, there is no maximum tem-perature, ~u-t we have found that -there is no reason to exceed 1000C or 120~C. Since the reac-tion ~etween zinc oxide and chlorine or hydrogen chloride is an exothermi.c reaction, the temperature is relatively easy to maintain~
In the ~ollowing examples, one type of rubber was used as a starting material to produce the contaminated carbon black used in the preferred exemplary embodiments. However, it should be emphasized that the contaminated carbon black can be obtained from any source and the method of the present invention is use-15 ful in treating such carbon black. In the preferred exemplary embodiments, the carhon black contained approximately 6~, by weight, of zinc oxide and approximately 3%, by weiyht, of sulfur, the remaining part of the carbon black being carbon with minor amounts of other oxides such as calcium oxide. It must be kept in mind that because of the fact that the carbon black was pro-duced from the pyrolysis of scrap rubber, all the volatile material was removed from the rubber.
In general, the carbon black was produced as follows:
Raw rubber~ either per se or after being shredded and dried was fed into a rotating retort together with heat caxrying solids, the temperature of the solids being sufficient to heat the rubber to the pyrolysis temperature for a period o~ from about three minutes to -ten minutes, and preferrably, between ;, :
five and eight minutes. In ~eneral, the temperature o the heat carrying solids ~5 ahou-t 12QQF when entering the retort and the pyrolysis temperature reached by the rubber is between about 95QF to lOOQF. After pyrolysis has been completed, which pyrolysis was conducted in the a~sence of oxygen, the vapours produced therefrom (whlch are generally hydrocarbons) are sep-arated from the solid c~ar material which is composed of very fine particles having an average diameter of less than 1 micron, and usually less than Q.5 microns, said char material being sub-lQ stantially free of coke and nondecomposed rubber. As noted,this char material is primarily carbon black contaminated with a~out 6%, by weight, o~ zinc oxlde, and about 3%, by weight, of sulfur.
Because of the "dusting" problem noted hereinbefore, the fine particle sized carbon black is formed into pellets of about one-eight~ inch in diameter. The reaction temperature of from 750C to 1000C to 1200C can be obtained by either heating ~;
the carbon black in the reaction zone to the appropriate tempera-ture or heating the chlorine or hydrogen chloride to the appro-priate temperature, or both. In the preferred exemplary embodi-ments, we first heat the carbon black pellets, obtained as indi-cated above, to a temperature of about 375C in a nitrogen atmo~
sphere. The reason for using a nitrogen or inert atmosphere is to prevent oxidation of the carbon black thereby rendering the carbon black less useful for recycling purposes, as for example, adding the car~on black to rubber to produce rubber tires.
The react;on zone~ wit~in which the carbon black is placed is a horizontal or vertical furnace having a condenser :
: ' :~3~
at the e~it end of the urnace. The car~on black is firs-t heated, as noted above, i~ an inert at~osphere such as nitro~en to a temperature of 375C. After -this temperature was reached, chlorine was added to the reaction zone (furnace) so that the chlorine came into intimate con-tact with the pellets of carbon black placed in the reaction zone. Generally speaking, free chlorine did not appear until after about sixty to eighty minutes. In all of the examples, except for one of the tests conducted at 800C. r chlorine addition was continued for an ad-ditional twenty minutes after the appearance of free chlorine I and then the test was terminated. ~n one of the tests conducted at 800C., (in the following Table, Test No. 3), the test was immediately -ter~inated after the appearance of free chlorine ln the exit gas.
The following Table I indicates the témperature at which the test was conducted, the amount of carbon black, in parts by wei~ht, charged to the reaction zone, the amount of chlorine added, in parts by weiyht, and the lenyth of run in minutes.
Table I
Test No. l 2 3 4 Temperature, C. 750 800800 (no soak) 1000 Carbon Black 25 25 25 25 Chlorine ll ll 10 Length of Run94 80 80 80 It should be noted that in -testing for free chlorine yas, the test involved using a potassium iodide scrubber, which was attached to the condenser. The scrubber collected the gases ,, , --1 0--3~3 ~
comin~ o~f, to indicate when ~ree chlorine was present. Tenlper-atuxes at whIch the reactions were conducted were reached by heatIng the ~urnace -to the appropriate temperature, after the chlorine gas was actually introduced into the furnace.
In the ~ollowing Table II, the results oE the zinc ex-traction and sulfur extract:ion are shown in weight percentages.
The car~on filack in the feed-material contained 6.1~ weight per-cent zinc as zinc oxide and 3.06 weight percent sulfur.
Tahle II
SUMMAR~ OF CHLORINATION RESULTS OF CARBON BLACK
Test No. 1 2 3 4 T~rature, C. 750 800 800(no soak) 1000 ~ Zinc Extraction 99.3 99.6 99.3 9~.7 % Sulfur Extraction 52.5 37.4 33.5 40.9 As can be seen from Table II, almost all of the zinc was extracted and about fifty percent of the sulfur was extracted -~
from the carbon black. Moreover, the pelletized carbon black which was contacted with the chlorine, retained its physical shape and integrity and could be used, as suchl to produce rubber tires.
As has been noted before, volatile zinc and sulfur chlorides were produced in the reaction. The zinc chloride was recovered and separated from the sulfur chloride by fractional condensation. Usin~ such a method, all of the zinc chloride can be recovered and could be recycled to make useful products.
To remove the chlorine from the carkon blaGk, which is not absolutely necessary to rouse the carbon black, ammonia was added to the car~on black at 800C thereby removing all of the ' . .
' z chlo~ine retained in the carbon hlack~
Although in the preferred exemplary em~odiment, only chlorine was used, i.t is to be understood that gaseous, non aqueous hydrogen chloride can also he used wi-th similar results.
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Back~round of_the Invention;
As is known in the art, carhon black is a ver~ useful com~odity and IS obtained from many resources. Amony the valu-able uses o~ carbon black i5 in the production of rubber tires.
~s a matter of fact, outside of rubber, the major portion of rubber tires is carbon black, and it would be very desirable if such car~on black contained in rubber tires could be reused again. The recycling of carbon black and obtaining useful pro-ducts from rubber contained in tires serves a two~fold purpose:
first, it would conserve our valuable resources and, second, it would ease the problem of what -to do with discarded rubber tires.
For example, at least two hundred million rubber tires are dis-carded in the Uni-ted States every year. And, although such tires make up a relatively small fraction of the solid waste, tires are very difficult to dispose of.
When rubber tires are burned, they give off large quan-tities of unburned hydrocarbons which are highly visible and noxious. Moreover, the problem of disposing of scrap rubber tires is not solved by using the tires as land fill because tires are resistant to natural decomposition and eventually emerge at 20 the surface of the land fill where their appearance is objection-; able.
Another approach to the pro~lem of what to aO with discarded rubber containing carbon b~ack, for example, rubber tires, is to pyrolyze the rubber tires to obtain valuable hydro~
carbons therefrom. However, after the hydrocarbons are removed, a great deal of solid material remains, said solid material (usually called char) bein~ composed primarily of carbon black and inorganic material primarily composed of zinc and sulfur.
~2--~3 ~8~
Carbon black cannot be success~ully reused to make, for example, ruhher tires, unless such inarg~nic Inaterial is removed from the carbon hlack. Moreover, since the primary metal included within the inorganic ma-terial is zinc, normally as zinc oxide, it is desirable to remove -the zinc in order to render the solid char reusable in pxoducing rubber tires, and, at: the same time, re-covering the zinc in order to be able to reuse this valuable metal.
~ummary o~ the ~nvention:
_~_ ___ The present invention relates to a me-thod or process of removing zinc from carbon black (for example, char residue re-maining after pyrolyzing of scrap rubber) containing upwards of 3~ zinc, calculated as zinc oxide. Additionally, the present process provides for the recovery and reuse of the zinc as well as allowing the char, composed primarily of carbon black, to be reused, for example, in the production oE rubber tires or any other product using carbon black. In essence, the present in vention allows for the recycling of solid carbon black which is contaminated with zinc oxide and perhaps other inorganic ~ 2Q -materials~sùch as sulfur, calcium oxide, and very minox-arnounts of other metal.
It is therefore the primary object of the present inven-tion to disclose and provide a process for removing substantially all of the zinc or zinc oxide contained in carbon black in order to be a~le to recycle the carbon black and to recover the zinc contained in said carbon black.
~ further object of the present invention is to disclose ~ ~3~
and provide an economical process for ~ecycllng carhon black and retainlng zinc oxide h~r slmple and econo~lcal process wherein the car~on ~lack is merely con-tacted with a gas such as chlorine at a temperature of ~rom ahout 732C to 1000C or 1200C and separating -the volatile zlnc chlorlde formed thereby from the solid carbon black.
Other objec-ts of the present in~ention will be apparent to those skilled in the art from the following detalled descrip tion wherein all parts and percentages are by weight, unless lQ expressly stated otherwise, and all temperatures are in degrees centigrade unless expressly stated otherwise.
Description of the Preferred Embodimen'ts In the preferred exemplary embodiments, the present in-vention will be illustrated with char produced from scarp rubber, said char belng composed of primarily carbon black (e.g. from 60% to 70%~ by weight, of carbon black, to as high as 85~ to 90 carbon black). The remainder of the char is usually designated as ash and the predominant portion of ~he ash is zinc, as zinc oxide, and sulfur. That is to say, of the ash, at least 50%
thereof will be zinc, as zinc oxide, and sulfur. In general, the zinc oxide will comprise at least 3% of the total weight of the char and the sulfur will normally comprise at least 1% to 1 2% of the char. In the preferred exemplary embodiments, the char used is obtained by pyrolyzing scrap rubber by contacting the rubber with heat carrying solids in a rotating retort.~
During the pyrolysis step, because of the rotation of the retort, ~, ' the heat carrylng sol~ds ('which are preferrably ceramic~ are mixed with the rubber so that not only is the heat transferred ~' ,~ `
from the hea-t carr~in~ sol.ids to -the rub.ber hu-t the rubber is ground so tha-t the sol:id remaining a-ter the pyrolysis and grinding step is of very fine particle size. ~ecause of this very fine particle size, there is a problern with "dusting".
Therefore, it is normal, in order -to prevellt "dusting", to make pellets of the finely divided particles of carbon hlack. Sur-prisingly, the present invention can remove, ~or example, the zinc oxide, from such.carbon black pellets and not adversely af-fect the physical integrity of the pelletized carbon black.
lQ That is, after pelletized carbon black is subjected to the in-stant process, the pelletized carbon black does not lose its shape or form; however, it should be noted that the pelletized carbon black may lose some of its strength bu-t not in such an amount that dusting is a problem.
The objects o-f the present invention are accomplished by contacting carbon black, contaminated with zinc oxide and sulfur, wherein the carbon black is either in finely divided form or in pelletiæed form, ~ith non-aqueous chlorine gas or hydrogen chloride gas at a temperature of at least ahout 732C, and pref-errably, 750C to about 1000C or 1200C. Surprisingly, using either chlorine gas or hydrogen chloride gas at such tempera-tures removes at least 18% of the zinc contaminating the carbon black and in actual practice, over 99%, by weight, of the zinc was removed utilizing the process of the present invention. Sub-stantially all of the zinc removed can be recovered and recycled.
The amount of chlorine gas or hydrogen chloride gas used Ln purifying the carbon black contaminated with zinc or zinc oxide can vary widely, but since one of the objects oE the ' 3~
present invention is to :insure that all, or suhstantially all, of the zi:nc o~ide or ZInC iS removed, it is therefore desi.rable if at least a stochiome-tric a~ount o:E chlorine gas or hydrogen chloride gas is allowed to contact the carbon black. It is pre~erred if a stochiometric excess of chlorille contacts the carbon black. The actual amount oE chlorine which should con-tact the carbon ~lack can he determined by testing the vapo~s given off with potass~um iodide which will indicate when free chlorine is present in the volatile gas. If such occurs, then lQ this indicates that substantially all of the zinc or zinc oxide has ~een removed as a volatile zinc chloride salt.
The reaction between zinc oxide and chlorine, in the presence of car~on, is as fo].lows: 3ZnO ~ 3C12 ~ 2C --~3ZnC1 CO ~ CO2. Thus, i-t can be seen that for one mole of zinc oxide present in the ash, at least one mole of chlorine shoul~ be used.
Stated differently, for every one hundred parts, by weight, of zinc oxide, at least about ninety parts, by weight, of chlorine should be used~ However, since the zinc oxide is present in I relatively small amounts, some of the chlorine will not react 2a with the zinc oxide, at least equal amounts of chlorine should be used based on the weight of the zinc oxide present.
We have found that, in general, for every one hundred parts of carbon black containing at least 3%, by weight, o-E
zinc, calculated as zinc oxid.e, there should be used at least twenty parts, by weight, of chlorine, and preferrably, at least thirty or forty parts by weight, of chlorine. There is no ma~i-mum amount of chlorine that should be used since, on~e the re-action is complete, it makes no difference if more chlorine is ~6--~3~
added except, o~ course, it is uneconomical. However, from a practical standpoint, we have ~ound that, in ~eneral, no more than one hundred parts need be used for each one hunclred parts, by ~eight, of car~on ~lack containing the zinc. The reason that S more -than a stochtometric excess of chlorine is desirable is hecause a certain amount is retained in the! carbon black and a certain amou.nt reacts with other oxides present in the carbon black reacting with khe zinc, and if present, the sulfurO The amounts indicated above also insure that subs-tantially all oE the 10. zinc oxide and sulfur, if present, is removed.
It should be noted that gaseous, non-aqueous hydrogen ; chloride works equally as well as chlorine in the present inven-tion. Moreover, the amount of hydrogen chloride necessary to be used in the present invention is about the same as the amount of chlorine gas since the molecular wéight of hydrogen chloride is about half as great as chlorine gas and because hydrogen chloride provides half as much chlorine as gaseous chlorine does. Thus, from a practical standpoint, at least about twenty parts, by weight of hydrogen chloride should be used for each one hundred parts,-by weight oE carbon black containing zinc oxide, and sometimes s~lfur. It is preferrable if at least thirty parts, by weight, or forty parts, by weight, of hydrogen chloride is used for each.one hundred parts, by weight, of carbon black since this insures that substantially all of the zinc and sulfur, : 25 if present, is remo~ed from the carbon black. Also, as pointed out above with respect to the chlorine gas, we have ound that in general, the maximum amount of hydrogen chloride generally necessary is one hundred parts, by weight of chlorine for each :
, z one hundred parts of carhon b.l~ck.
A~ h~s been noted, -the temperature ~t which the non-aqueous ~aseous chlorine, or n~n-a~ueous, gaseous hydrogen chloride contacts -the carhon black should be at least 732C.
~rom purely t~eoretical consideration, there is no maximum tem-perature, ~u-t we have found that -there is no reason to exceed 1000C or 120~C. Since the reac-tion ~etween zinc oxide and chlorine or hydrogen chloride is an exothermi.c reaction, the temperature is relatively easy to maintain~
In the ~ollowing examples, one type of rubber was used as a starting material to produce the contaminated carbon black used in the preferred exemplary embodiments. However, it should be emphasized that the contaminated carbon black can be obtained from any source and the method of the present invention is use-15 ful in treating such carbon black. In the preferred exemplary embodiments, the carhon black contained approximately 6~, by weight, of zinc oxide and approximately 3%, by weiyht, of sulfur, the remaining part of the carbon black being carbon with minor amounts of other oxides such as calcium oxide. It must be kept in mind that because of the fact that the carbon black was pro-duced from the pyrolysis of scrap rubber, all the volatile material was removed from the rubber.
In general, the carbon black was produced as follows:
Raw rubber~ either per se or after being shredded and dried was fed into a rotating retort together with heat caxrying solids, the temperature of the solids being sufficient to heat the rubber to the pyrolysis temperature for a period o~ from about three minutes to -ten minutes, and preferrably, between ;, :
five and eight minutes. In ~eneral, the temperature o the heat carrying solids ~5 ahou-t 12QQF when entering the retort and the pyrolysis temperature reached by the rubber is between about 95QF to lOOQF. After pyrolysis has been completed, which pyrolysis was conducted in the a~sence of oxygen, the vapours produced therefrom (whlch are generally hydrocarbons) are sep-arated from the solid c~ar material which is composed of very fine particles having an average diameter of less than 1 micron, and usually less than Q.5 microns, said char material being sub-lQ stantially free of coke and nondecomposed rubber. As noted,this char material is primarily carbon black contaminated with a~out 6%, by weight, o~ zinc oxlde, and about 3%, by weight, of sulfur.
Because of the "dusting" problem noted hereinbefore, the fine particle sized carbon black is formed into pellets of about one-eight~ inch in diameter. The reaction temperature of from 750C to 1000C to 1200C can be obtained by either heating ~;
the carbon black in the reaction zone to the appropriate tempera-ture or heating the chlorine or hydrogen chloride to the appro-priate temperature, or both. In the preferred exemplary embodi-ments, we first heat the carbon black pellets, obtained as indi-cated above, to a temperature of about 375C in a nitrogen atmo~
sphere. The reason for using a nitrogen or inert atmosphere is to prevent oxidation of the carbon black thereby rendering the carbon black less useful for recycling purposes, as for example, adding the car~on black to rubber to produce rubber tires.
The react;on zone~ wit~in which the carbon black is placed is a horizontal or vertical furnace having a condenser :
: ' :~3~
at the e~it end of the urnace. The car~on black is firs-t heated, as noted above, i~ an inert at~osphere such as nitro~en to a temperature of 375C. After -this temperature was reached, chlorine was added to the reaction zone (furnace) so that the chlorine came into intimate con-tact with the pellets of carbon black placed in the reaction zone. Generally speaking, free chlorine did not appear until after about sixty to eighty minutes. In all of the examples, except for one of the tests conducted at 800C. r chlorine addition was continued for an ad-ditional twenty minutes after the appearance of free chlorine I and then the test was terminated. ~n one of the tests conducted at 800C., (in the following Table, Test No. 3), the test was immediately -ter~inated after the appearance of free chlorine ln the exit gas.
The following Table I indicates the témperature at which the test was conducted, the amount of carbon black, in parts by wei~ht, charged to the reaction zone, the amount of chlorine added, in parts by weiyht, and the lenyth of run in minutes.
Table I
Test No. l 2 3 4 Temperature, C. 750 800800 (no soak) 1000 Carbon Black 25 25 25 25 Chlorine ll ll 10 Length of Run94 80 80 80 It should be noted that in -testing for free chlorine yas, the test involved using a potassium iodide scrubber, which was attached to the condenser. The scrubber collected the gases ,, , --1 0--3~3 ~
comin~ o~f, to indicate when ~ree chlorine was present. Tenlper-atuxes at whIch the reactions were conducted were reached by heatIng the ~urnace -to the appropriate temperature, after the chlorine gas was actually introduced into the furnace.
In the ~ollowing Table II, the results oE the zinc ex-traction and sulfur extract:ion are shown in weight percentages.
The car~on filack in the feed-material contained 6.1~ weight per-cent zinc as zinc oxide and 3.06 weight percent sulfur.
Tahle II
SUMMAR~ OF CHLORINATION RESULTS OF CARBON BLACK
Test No. 1 2 3 4 T~rature, C. 750 800 800(no soak) 1000 ~ Zinc Extraction 99.3 99.6 99.3 9~.7 % Sulfur Extraction 52.5 37.4 33.5 40.9 As can be seen from Table II, almost all of the zinc was extracted and about fifty percent of the sulfur was extracted -~
from the carbon black. Moreover, the pelletized carbon black which was contacted with the chlorine, retained its physical shape and integrity and could be used, as suchl to produce rubber tires.
As has been noted before, volatile zinc and sulfur chlorides were produced in the reaction. The zinc chloride was recovered and separated from the sulfur chloride by fractional condensation. Usin~ such a method, all of the zinc chloride can be recovered and could be recycled to make useful products.
To remove the chlorine from the carkon blaGk, which is not absolutely necessary to rouse the carbon black, ammonia was added to the car~on black at 800C thereby removing all of the ' . .
' z chlo~ine retained in the carbon hlack~
Although in the preferred exemplary em~odiment, only chlorine was used, i.t is to be understood that gaseous, non aqueous hydrogen chloride can also he used wi-th similar results.
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Claims (8)
- CLAIMS:
l. A method of purifying carbon black pellets contaminated with zinc without adversely affecting the carbon black pellets, characterized by the following steps:
(a) forming carbon black pellets from very fine carbon black particles having an average diameter of less than one micron and contaminated with at least 3%, by weight, of zinc, calculated as zinc oxide, (b) contacting said contaminated carbon black pellets at a temperature of at least 732°C. with a non-aqueous gas selected from the group consisting of chlorine and hydrogen chloride thereby forming gaseous zinc chloride; and (c) separating the gaseous zinc chloride from the carbon black pellets. - 2. A method according to claim 1, characterized by said temperature of contact is from 732°C. to 1200°C.
- 3. A method according to claim 2, characterized by said temperature of contact is from 750°C. to 1000°C.
- 4. A method according to claim 1, characterized by the amount of non-aqueous gas is at least 20 parts, by weight, based on 100 parts, by weight, of the carbon black.
- 5. A method according to claim 4, characterized by the amount of non-aqueous gas is from 20 parts, by weight, to 100 parts, by weight, based on 100 parts, by weight, of the carbon black.
- 6. A method according to claim 1, characterized by the non-aqueous gas is chlorine.
- 7. A method according to claim 1, characterized by the carbon black pellets are also contaminated with at least 1%, by weight, of sulfur; sulfur chloride is formed during the contacting step; and the sulfur chloride is separated along with the gaseous zinc chloride from the carbon black pellets.
- 8. A method according to claim 7, characterized by the following additional step:
(d) separating the zinc chloride from the sulfur chloride.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA364,920A CA1131882A (en) | 1980-11-18 | 1980-11-18 | Method for easily removing zinc from carbon black contaminated with zinc |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA364,920A CA1131882A (en) | 1980-11-18 | 1980-11-18 | Method for easily removing zinc from carbon black contaminated with zinc |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131882A true CA1131882A (en) | 1982-09-21 |
Family
ID=4118486
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA364,920A Expired CA1131882A (en) | 1980-11-18 | 1980-11-18 | Method for easily removing zinc from carbon black contaminated with zinc |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1131882A (en) |
-
1980
- 1980-11-18 CA CA364,920A patent/CA1131882A/en not_active Expired
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