Abstract:
A method of producing activated carbon from lignite, in which pit-wet lignite is heated to high temperatures. The invention further describes the heating of the lignite in the presence of additional water vapor. The invention also contemplates the addition of potassium ions to the lignite, in the form of potassium hydroxide.

Description:
This specification is a continuation of Ser. No. 07/742,516 filed Aug. 6, 1991, which is a continuation of Ser. No. 07/544,459 filed Jul. 19, 1990, which is a continuation of Ser. No. 07/415,979 filed Oct. 3, 1989, all now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a method of producing activated carbon based on lignite [brown coal]. 
     The production of activated carbon from lignite is known. Such known methods are described in the following documents: 
     D. J. McCarthy, Carbon 15 (1977), pp. 95-101. 
     Lignite is dried and briquetted. The lignite briquettes are comminuted again and activated with water vapor in a countercurrent. 
     R. A. Durie et al, Fuel 58 (1979), pp. 472-476. 
     The lignite is subjected to an acid washing and an ion exchange, dried in air, optionally granulated, carbonized and activated with water vapor. 
     L. J. Harner et al., Proc.-Int. Conf. Coal Res. 5th, 1980, 805-19/CA 90: 74826Y. 
     The lignite is predried to a moisture content of approximately 16% by weight and briquetted. The briquettes are comminuted again, carbonized and activated with water vapor. 
     A. Albiniak et al., Pr. Nauk. Inst. Chem. Technol. Nafty Wegla Politech. Wroclaw 41 (1985) 213-8 / CA 104: 209 764 n. 
     The lignite is dried, coked and subsequently activated with water vapor, carbon dioxide and oxygen. 
     DE-OS 36 03 003. 
     The lignite is dried, pyrolized at 350°-500° C. and activated with water vapor at 700°-800° C. 
     DDR-PS 207 183. 
     The lignite is dried to a moisture content of 20%, extracted with organic solvents, dried in air, subsequently mixed with sawdust and zinc chloride solution, granulated and heated to 600°-750° C. 
     DDR-PS 211 331. 
     The lignite is predried, mixed with sawdust and/or peat as well as hydrochloric zinc chloride solution, granulated and heated to 650°-750° C. 
     DDR-PS 227 946. 
     The lignite is dried and pressed to blanks, the blanks are comminuted, the comminuted blanks are finally pressed to blanks again, the finally-pressed blanks are degassed, comminuted and activated in known activating reactors. 
     EP-PS 2275 and EP-PS 2674. 
     The lignite is subjected to an acid and water washing, dried, ground and briquetted. The briquettes are comminuted, carbonized (at a low temperature) and activated. 
     Kirk-Othmer, Encyclopedia of Chemical Terminology, 3rd Edition, Vol. 4, pp. 561-569, &#34;Activated Carbon&#34; also describes some prior art methods of processing lignite into activated carbon. 
     These prior art references show the background methods and are herein incorporated in their entirety. 
     The known methods have the disadvantage that numerous method steps are required, for example, water and acid washing, drying, grinding, briquetting and coking of the lignite are necessary as a pretreatment of the lignite. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to provide a method of producing activated carbon from lignite. The method is featured by heating pit-wet lignite to rather high temperatures, optionally, with the addition of potassium ions. 
     The term &#34;pit-wet lignite&#34;, as used in this specification, means a lignite which is processed immediately after its removal from the mine, without altering its natural water content, in accordance with the method of the invention. 
     In individual instances the water content of the pit-wet lignite may be lowered by drying to an amount of 30% by weight. This drying can be accomplished with driers that are known in the art. 
     However, drying adversely affects the adsorption capacity of the final product produced from a partially predried lignite. 
     The temperature to which the pit-wet lignite is heated can be greater than 600° C., and preferably greater than 800° C. It is advantageous to add additional water vapor during the heating of the pit-wet lignite. It is also advantageous to add additional potassium ions in aqueous solution during the heating of the pit-wet lignite. 
     The method of the invention has the advantage that activated carbon can be produced from pit-wet lignite in a single method step. 
     The method of the invention can be carried out in known activating devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantageous features of the invention will be more fully appreciated when viewed with the accompanying drawings wherein: 
     FIG. 1 is a plot showing the relationship between the iodine value and the water content of the pit-lignite; and 
     FIG. 2 is a plot of the iodine value vs. the water content of a stepwise dried lignite. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Examples 
     Five different lignites A, B, C, D and E whose properties are listed in table 1 were used for the tests. 
     The lignites, supplied in a pit-wet and coarse state, were broken in a jaw crusher and sieved to a fraction of 1-4 mm, depending upon the rotating cylinder kiln used. The heating of the lignites took place in the indirectly heated rotating cylinder kiln under variation of the temperature, variation of the water content, variation of the gaseous atmosphere and variation of the potassium content. 
     Conditions 
     rotating cylinder kiln: indirectly heated 
     activating temperature: 600°-1000° C. 
     amount of water vapor: without water vapor, or 1000 g/h in reference tests 
     rpms: 7.5 rpms 
     retarding dam height: without retarding disk 
     dwell time: approximately 15 min. 
     cylinder inclination: approximately 1%. 
     The products were thoroughly washed with water and tested according to methods known in the art. 
     Raw material influences 
     The obtained adsorption capacity (iodine number) is a function of the original water content of the lignite. The adsorption capacity is improved as the water content of the pit-wet lignite increases (cf. FIG. 1 and Table 2). 
     Influence of the activating temperature 
     The influence of the temperature was tested in a range of 600°-1000° C. (cf. Table 3). Again, adsorption capacity improves with the increase in activation temperature, as evidenced by the increase in iodine number. 
     Influence of the drying 
     In order to test the influence of drying on the adsorption capacity, lignite D was dried in stages. The inverse method of first completely drying the lignite and adjusting the water content by means of the addition of water is not possible. When the water content of lignite is reduced, the adsorption capacity is impaired (FIG. 2 and Table 4). 
     Addition of vapor 
     In the comparison of pit-wet lignite without the addition of water vapor to dried lignite with the addition of water vapor, the dried lignite yields activated carbons with considerably worse adsorption properties at approximately the same yield. If pit-wet lignite is used, the adsorption capacity can be positively influenced by an additional supplying of water vapor (Table 5). 
     Tests under potassium catalysis 
     The pit-wet lignites were sprayed with potash lye, which slightly raised the water content of the lignites. The addition of potassium (1.0% by weight KOH and onto dry carbon) resulted in a distinct increase of the number of fine pores in the products (cf. Table 6). 
     The influence of the potassium concentration in a range of 0 to 2.0% by weight KOH (and onto dry carbon) was tested using lignite C. It can be shown using the benzene isotherm that as the potassium content increases, the number of mesopores decreases and the number of micropores increases (cf. Table 7). 
     While the invention has been described with particular examples and embodiments, various modifications may be made without departing from the spirit and scope of the claims. 
     
                                           TABLE 1__________________________________________________________________________Properties of lignite                                      Maceral     Vola-                            group  Ash     tile   Elementary                analysis  con-     con-         C- composition               huminite   Water  tent     tent         fixed            C   H   N   O   S   Atomic                                      liptinite                                             Pore                                                 TrueLig-   content  %  %   %  %   %   %   %   %   proportions                                      inertinite                                             volume                                                 density                                                     Porositynite   wt. %  (wf)     (wf)         (wf)            (waf)                (waf)                    (waf)                        (waf)                            (waf)                                H/C                                   O/C                                      % %  % ml/g                                                 g/ml                                                     Vol.__________________________________________________________________________                                                     %A  46  10.2     67.4         22.4            71.1                6.5 1.1 20.6                            0.56                                1.09                                   0.22                                      95                                        4  1 0.238                                                 1.634                                                     28.0B  49  7.1     77.8         15.1            71.1                7.2 1.2 20.2                            0.25                                1.21                                   0.21                                      82                                        11 7 0.277                                                 1.535                                                     29.8C  51  5.3     56.1         38.6            73.5                7.8 1.2 16.8                            0.48                                1.26                                   0.17                                      92                                        5  3 0.390                                                 1.594                                                     38.3D  56  2.0     61.4         36.6            72.7                6.6 1.1 19.0                            0.40                                1.09                                   0.20                                      92                                        5  3 0.262                                                 1.506                                                     29.1E  59  0.9     58.3         40.8            65.3                6.6 1.2 26.4                            0.45                                1.21                                   0.30                                      85                                        10 5 0.714                                                 1.520                                                     52.0__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________Variation of the raw materialActivating temperature: 950° C.carbon storage: 300 g/h and onto dry carbon           Benzene           MethyleneWater     Furnace           isotherm AS   Iodine                             blue  Molassescontent % yield %           (% by weight) value                             titer mgLignite    weight     by weight           9/10              1/10                 1/100                     1/1000                         mg/g                             ml/0.1 g                                   value__________________________________________________________________________A   46    9.1   56.6              18.4                 11.4                     5.9 585 11.0  195B   49    17.4  49.0              17.8                 11.9                     7.4 595 11.0  215C   51    9.2   45.3              18.3                 12.0                     7.4 660 11.5  200D   56    9.4   52.1              22.8                 16.0                     9.4 865 13.5  180E   59    13.9  55.7              29.9                 23.0                     14.1                         1050                             15.5  190__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________Variation of the activating temperatureLignite DWater content: 56% by weightCarbon charge: 375 g/h and onto dry carbon        Benzene           MethyleneActivating  Furnace        isotherm AS   Iodine                          blue  Molassestemperature  yield %        (% by weight) value                          titer mg value°C.  by weight        9/10           1/10              1/100                  1/1000                      mg/g                          ml/0.1 g                                mg__________________________________________________________________________600    42.1   0.9            0.3               0.2                  --   55 0.5   &gt;3000700    27.2  14.3           11.0               8.8                   6.8                      295 0.5   &gt;3000800    27.4  39.4           17.3              12.2                   8.0                      590 6.0   360850    24.5  39.7           20.0              14.7                   9.9                      670 6.0   370900    21.2  43.3           20.8              15.3                  10.1                      725 6.0   295950    12.1  52.9           23.7              17.1                  10.9                      835 9.0   2151000    6.0  58.8           24.3              17.3                  10.8                      790 10.5  170__________________________________________________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________Variation of the water contentLignite DActivating temperature: 950° C.Carbon charge: 300 g/h and onto dry carbonWater      Benzene           MethyleneContentFurnace      Isotherm AS   Iodine                        blue  Molasses% by yield %      (% by weight) value                        titer valueweightby weight      9/10         1/10            1/100                1/1000                    mg/g                        ml/0.1 g                              mg__________________________________________________________________________&lt;1   38.3  14.2          6.8             5.5                4.1 275 2.0   2800 7   33.1  23.9         10.1             8.0                6.3 375 2.5   68516   27.8  23.8         11.4             9.6                7.4 380 3.0   91520   29.5  30.4         14.5            11.2                8.7 475 3.5   52026   25.4  35.0         16.7            12.8                9.7 535 4.5   44032   17.9  44.5         20.2            15.5                10.8                    675 7.5   35046   16.5  48.8         22.8            17.0                11.5                    790 8.5   28556    9.4  52.1         22.8            16.0                9.4 865 13.5  180__________________________________________________________________________ 
    
     
                                           TABLE 5__________________________________________________________________________Influence of the addition of vaporLignite DActivating temperature: 950° C.WaterContent              Benzene           Methyleneof the    Addition          Furnace                Isotherm AS   Iodine                                  blue  MolassesligniteCarbon     of vapor          yield %                (% by weight) value                                  titer value% by wt.g/h (TS)     g/h  weight                9/10                   1/10                      1/100                          1/1000                              mg/g                                  ml/0.1 g                                        mg__________________________________________________________________________&lt;1   300  --   38.3  14.2                    6.8                       5.5                          4.1 275 2.0   2800&lt;1   300  1000  8.8  35.4                   15.1                      10.7                          6.4 570 8.0   33556   300  --    9.4  52.1                   22.8                      16.0                          9.4 865 13.5  18056   900  --   26.9  29.5                   17.8                      14.3                          10.2                              610 4.0   96556   900  1000 19.6  47.1                   21.9                      15.6                          9.9 790 9.5   320__________________________________________________________________________ 
    
     
                                           TABLE 6__________________________________________________________________________Variation of the raw material under potassium catalysisActivating temperature: 950° C.Carbon charge: 600 g/h and onto dry carbon                Benzene           MethylenePotassium Water          Furnace                Isotherm AS   Iodine                                  blue  Molassescontent % content          yield %                (% by weight) value                                  titer valueLignite    weight     % by wt.          weight                9/10                   1/10                      1/100                          1/1000                              mg/g                                  ml/0.1 g                                        mg__________________________________________________________________________A   --    46.0 16.2  43.3                   18.4                      11.0                           6.6                              595  9.0  190A   1.0   49.1 13.0  58.2                   24.1                      14.5                           7.3                              690 12.5  155B   --    49.0 22.4  37.2                   18.6                      12.7                           8.6                              610  8.0  280B   1.0   51.9 19.2  51.2                   24.9                      17.5                          11.3                              830 13.0  230C   --    51.0 15.4  56.5                   20.0                      13.3                           8.9                              665 10.5  190C   1.0   53.4 14.1  60.4                   30.6                      20.8                          11.6                              995 12.5  155E   --    59.0 21.7  44.3                   28.9                      23.4                          15.3                              1035                                  13.0  415E   1.0   57.0 22.5  47.3                   39.2                      31.5                          19.2                              1260                                  18.5  &gt; 3000__________________________________________________________________________ 
    
     
                                           TABLE 7__________________________________________________________________________Variation of the potassium contentLignite CActivating temperature: 950° C.Carbon charge: 600 g/h and onto dry carbon             Benzene           Methylene  Water       Furnace             Isotherm AS   Iodine                               blue  MolassesKOH content  content       yield %             (% by weight) value                               titer value% by weight  % by wt.       weight             9/10                1/10                   1/100                       1/1000                           mg/g                               ml/0.1 g                                     mg__________________________________________________________________________--     51.0 15.4  56.5                20.0                   13.3                        8.9                           665 10.5  1900.5    53.6 11.9  55.8                24.1                   16.9                       10.8                           780 13.0  2001.0    53.6 14.1  60.4                30.6                   20.8                       11.6                           995 12.5  1551.5    53.6 13.8  62.6                36.3                   21.5                        9.4                           1200                               18.0  1502.0    53.6 14.1  60.9                38.1                   22.3                       10.4                           1095                               17.5  325__________________________________________________________________________