(19)
(11) EP 0 000 214 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
10.01.1979 Bulletin 1979/01

(21) Application number: 78200033.5

(22) Date of filing: 09.06.1978
(51) International Patent Classification (IPC)2B01J 20/20, C01B 31/12
// C02F1/28
(84) Designated Contracting States:
BE DE FR GB NL

(30) Priority: 22.06.1977 NL 7706879

(71) Applicant: AKZO N.V.
NL-6824 BM Arnhem (NL)

(72) Inventor:
  • De Jong, Geert Jan
    7548 PN Boekelo (NL)

(74) Representative: Sieders, René 
AKZO NOBEL N.V. Patent Department (Dept. CO) P.O. Box 9300
6800 SB Arnhem
6800 SB Arnhem (NL)


(56) References cited: : 
   
       


    (54) Process for the preparation of a solid carbon-containing material having a sorption capacity for metal ions.


    (57) Process for the preparation of a solid carbon-containing material having a sorption capacity for metal ions.
    The invention concerns a process of preparing solid metal sorbents from cheap carbonaceous material, like rubber waste, peat, coal or petroleum coke. The material is first mixed with sulphur and heated at 120-500°C and then subjected to a treatment with an aqueous alkali solution.
    Optionally and prior to the latter treatment a moderate oxidizing step is included. The resulting solid product is an excellent metal sorbent for effluent treatment and the like.


    Description


    [0001] The invention relates to a process for the preparation of a solid carbon-containing material having a sorption capacity for metal ions. The preparation of a solid carbon-containing material having a sorption capacity for metal ions is known in itself. In the Netherlands Patent Application 6 805 305, for instance, a process is described in which polymers of vinyl aromatic hydrocarbons are reacted with a compound made up of sulphur and chlorine in the presence of a catalyst and the resulting polymer sulphides or polymer polysulphides are oxidized or reduced.. Reduction results in the formation of thiol resins which have a high affinity for ions of heavy metals. A disadvantage to the known metal adsorbing material is its high price. This is due both to the high price of the starting materials and the relatively complex process to be used for the preparation of the desired thiol resins.

    [0002] Particularly, when a material is considered which does not qualify for regeneration once it is spent, the known process must be regarded as costly.

    [0003] Surprisingly, is has now been found that a solid carbon-containing material having a sorption capacity for metal ions can be obtained in an inexpensive and simple manner by mixing the carbon-containing starting material with sulphur, heating the mixture for some time to a temperature of about 120o-500o C., and subsequently treating it with an aqueous solution of alkali metal hydroxide an a temperature not exceeding about 200° C. Tt should be

    [0004] treatment with sulphur of a carbon-containing starting material, viz. a synthetic rubber and/or natural rubber, in order to obtain an active carbon is known in itself from the Netherlands Patent Applicaticn 7 210 632. Besides sulphur, however, a great many inorganic and organic compounds are mentioned, the use of which is apparently preferred since no example is given in which sulphur is employed. After pyrolysis the resulting active carbon can be further activated by burning the carbon. Both from the way in which further activation takes place and from the applications mentioned, such as the treatment of water, sugar juices, etc., it further appears that for the active carbon described in the last-mentioned patent application a mainly physical adsorption is envisaged.

    [0005] For the process according to the invention various carbon-containing starting materials may be used. As examples of suitable materials may be mentioned waste materials such as waste rubber, but also peat, liqnite, coal, asphalt or petroleum coke. They are preferably used in a finely divided state, in the form of for instance chips or grains having a diameter of not more than a few millimeters. The rubber to be used may be of synthetic or natural origin. It will generally occur in the form of worn tyres of automobiles or other motor vehicles or means of transport, and in the form of worn objects that are partly or entirely made of rubber, such as conveyor belts. The rubber objects may be cut up or ground in any convenient manner, possibly after removal of metal parts, for instance from the beads of automobile tyres. The process according to the invention is usually so carried out that before, during or after the carbon-containing starting material is cut up, it is mixed with 0.1 to 5 parts by weight of sulphur and subsequently heated for a number of hours in an oven at a temperature in the range of about 120 to 500o C. Preference, however, is given to a treatment with 0.5 to 1.5 parts by weight of sulphur per part by weight of starting material at a temperature between about 200 and 300o C. '

    [0006] The subsequent treatment of the sulphurized material with an aqueous solution of an alkali metal hydroxide can suitably be carried out at a temperature not exceeding about 200 C.; above 100 C.the treatment is usually done in an autoclave. It is preferred that use should be made of a sodium hydroxide solution, for instance a 10% NaOH solution, by which with proper stirring the treatment can be completed within a few hours at a temperature of 800C. or higher.

    [0007] It has further been found that in the treatment with an aqueous sodium hydroxide solution the formation of thiol groups can still be considerably furthered when in the sodium hydroxide solution there is also dissolved an alkali metal sulphide. Depending on the amount of sulphur previously added to the starting material such a sulphide solution may already be sufficiently formed in situ, so that the sodium hydroxide solution used also may with advantage be employed for treating a fresh batch. In many cases, however, it is advisable, that the sulphide should be dissolved in the aqueous sodium hydroxide solution beforehand, for instance 10% Na2S in a 10% NaOH solution.

    [0008] The material successively treated with sulphur and an aqueous solution of NaOH is finally filtered and/or washed with (acidified) water, after which it is ready for use.

    [0009] The physical appearance of the novel adsorbing materials according to the invention may vary from gel form to porous solid matter.

    [0010] For example the material obtained by treating cut up automobile tyres at a temperature between 180o and 280o C.has a gel like structure. Treatment of the same starting material at a temperature above 400° C. results in obtaining a material having a porous structure.

    [0011] The material produced with the process according to the invention not only shows the property of a cation exchanger, but is also capable of binding metals that occur in the form of anionic complexes.

    [0012] Moreover, the material according to the invention appears to have a high reducing capacity, which is particularly manitest in the sorption of ions of noble metals, such as gold and silver, and cf metals of the platinum group. It is also found possible for instance to reduce Cr042- to Cr3+. This means that the novel material according to the invention can also be looked upon as an inexpensive reducing agent. Another useful application of the material according to the invention consists in the removal of mercury from concentrated sulphuric acid, as obtained by roasting zinc sulphide.

    [0013] 

    from it, if desired, by dry distillation.

    [0014] It has further been found that the practical applicability of the material prepared by the process according to the invention can still be considerably improved upon.

    [0015] To that end the invention also provides a process in which prior or subsequent to thermal treatment the starting material is subjected to a treatment with sulphur or oleum, or still heated in the presence of air or some other oxygen-containing gas.

    [0016] By this additional treatment there are introduced a small number of more or less polar groups such as sulphonic acid groups and/or carboxyl groups, which promote the swelling cf the material in water. In practice the treatment with sulphuric acid will as a rule be carried out by bringing 1 part by weight of the material to be treated into contact for some time with 1 to 4 parts by weight of 96% by weight H2S04, Upon completion of the reaction the material is centrifuged and washed with water. It is preferred that the treatment with air should take place in a fluid bed. The present invention will be further described in the following examples. These examples are, of course, only meant to illustrate and not to limit the invention.

    Example 1



    [0017] By cutting up old autombile tyres rubber chips measuring 1 to 2 mm were obtained. Of these chips 100 parts by weight were mixed with 120 parts by weight of sublimed sulphur. The resulting mixture was subsequently heated in a rotating steel oven for eight hours at a temperature of 230° C. Next, the temperature was increased to 280° C. over a period of 8 hours. There were obtained 130 parts by weight of hard grains.

    [0018] Half of the resulting material, while in the fluidized state was subsequently heated in air at 350o C. over a period of 6 hours and thereafter stirred for 4 hours at 30o C. in an aquecus solution containing 10% NaOH and 10% Na2S. The chips were then filtered off and washed with water. After the material had been acidified with a solution of 5% by wieght and washed with water, a product IA was obtained whose ien exchanging properties are given in Example VI and Example IX. The other half of the material, instead of being heated in air, was heated for 4 hours to 90°C. with stirring in the presence per part by weight of. granules of 3 parts by weight of concentrated (95% by weight) sulphuric acid. After the acid had been washed out with water, the same treatment was carried out as described above for the first batch of chips. The ion exchanging properties of this product IB are given in Example VII and Example IX.

    Example II



    [0019] Brown coal briquettes were crushed and ground into grains measuring 1 to 2 mm.

    [0020] After drying in an oven at 105o C.100 parts by weight of the grains made up of brown coal and pitch were mixed with 50 parts by weight of sulphur and introduced into a rotating steel oven whose temperature was raised to 350o C.over a period of 4 hours. There were obtained 90 parts by weight of hard grains which were heated for 2 hours at 900 C in an aqueous solution containing 10% by weight of NaOH.

    [0021] The grains, which had strongly swollen in the aqueous NaOH solution, were successively washed with water and acidified with dilute sulphuric acid (5% by weight of H2SO4). After they had again been washed with water, their properties were determined. The results are given in Example VIII and Example IX.

    Example III



    [0022] 100 parts by weight of coal grains (containing 24% volatile material) measuring 1 to 2 mm were mixed with 100 parts by weight of sulphur and subsequently heated for 8 hours in a rotating steel oven, with the temperature being gradually raised from 120°C to 300° C.

    [0023] After cooling it was found that the yield of





    [0024] the mixture thus obtained was heated for 4 hours at 300° C. Finally, the resulting grains were still heated for 5 hours at 90 C.with an aqueous solution of 10% by weight NaOH and 10% by weight Na2S. Next, as in Example III, the grains were successively washed with water, excess acid and water.

    [0025] The results are given in Example IX.

    Example V



    [0026] 100 arts by weight of asphalt were heated, with stirring, with 100 parts by weight of sulphur. At a temperature of 200° C.H2S escaped. Upon continued heating to 260° C the viscosity of the mass increased. 4 hours the mass was left to cool down, followed by crushing it into grains measuring 0.5 to 1.5 mm. Subsequently, 100 parts by weight of the sulphurized material were treated for 16 hours at 100° C. with 200 parts by weight of 96% by weight H2SO4. After the material had been cooled and the concentrated H2SO4 been centrifuged off, it was washed with water until acid free and treated with an aqueous NaOH/Na2S solution in the way indicated in Example IV. NaOH/Na2 S solution in the way indicated in Example IV.

    [0027] Upon analysis it was found that this material contained strongly acid groups in an amount of as little as 50 meq/l. When 25 ml of grains had been introduced into a 20 cm column, they were found capable of sorbing all silver from a fixing bath containing 1 g Aq per litre.

    Example VI



    [0028] To illustrate the strong metal adsorbing capacity of the material prepared by the process according to the invention the product prepared in Example I A was tested for its capacity of retaining mercury from a HgCl4 ions-containing solution.

    [0029] Hg Cl4 2- ions-containing solution.

    [0030] Through a column of the product prepared in Example I A 20 cm in bed weight and having a bed volume of 25 ml there was passed an aqueous solution containing 100 mg Hg 2+ and 10 grammes of NaCl per litre.

    [0031] Over a period of 30 hours 10 titres of 400 bed volumes of this solution were passed through the column. Next, it was found upon analysis by flame spectrometry that the effluent still contained only as little as about 1 ppb (part per billion) of mercury. Comparative experiments in which use was made of frown coal briquettes (particle size 0.5 to 1.5 mm) treated with an aqueous solution of NaOH and of coal grains also areated with such a solution and fluidized in air ("Oxycoal") yielded



    [0032] These materials, however, were not capable of retaining mercury a Hg Cl4 ions-containing solution.

    [0033] This capacity is not obtained until the material has been


    Example VII



    [0034] The product prepared in Example I B was introduced into a 20 cm as used in Example VI. Through the column there was passed a sulchirie acid solution (pH = 1) containing chromium in the form of Cro. in an amount of 35 mg/l. After the passage of 20 litres or 800 volumes the yellow solution was still found to get entirely


    Example VIII



    [0035] 25 ml of granular material prepared in the way described in Example It were introduced into a 20 cm column, as used in Example VI

    Through the column there was passed a solution of 1 mg Cu in 25% by weight sulphuric acid. After a passage of 40 bed volumes over a period of 8 hours no copper could be found in the effwens of the column.

    [0036] The solution was subsequently replaced by a 5% sulphurie acid

    containing about 100 mg Ag per litre.

    [0037] Here too, after a passage of 1 litre over a period of 9 hours, silver could be detected in the effluent of the column, Finally, the silver solution was replaced by a sulphuric acid gold solution (about 100 Au 3+ per litre). After 1 litre of this solution nad (about 100 mg Au per litre) . After litre of this solution nad been passed through over a period of 8 hours, this metal ion

    found to be completely adsorbed. The sorptions were attended

    reduction of the metal ions.

    Example IX



    [0038] 



    [0039] 




    Claims




     
    2. A process according to claim 1, characterized in that in whe aqueous solution used there is also dissolved an alkali metal sulphide.
     
    3. A process according to claim 1, characterized in that before en after the thermal treatment the starting material is subjested to a treatment with sulphuric acid or oleum or heated in the presence of air or some other oxygen-containing gas.
     





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