Patent Publication Number: US-5292708-A

Title: Method of producing activated carbon from pit-wet lignite

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                    
                                                      True                
Lig-                                                                      
   content                                                                
       %  %   %  %   %   %   %   %   proportions                          
                                           inertinite                     
                                                  volume                  
                                                      density             
                                                          Porosity        
nite                                                                      
   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               
                                                          28.0            
B  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               
                                                          29.8            
C  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               
                                                          38.3            
D  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               
                                                          29.1            
E  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 material                                             
Activating temperature: 950° C.                                    
carbon storage: 300 g/h and onto dry carbon                               
                Benzene           Methylene                               
Water     Furnace                                                         
                isotherm AS   Iodine                                      
                                  blue  Molasses                          
content % yield %                                                         
                (% by weight) value                                       
                                  titer mg                                
Lignite                                                                   
    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  195                               
B   49    17.4  49.0                                                      
                   17.8                                                   
                      11.9                                                
                          7.4 595 11.0  215                               
C   51    9.2   45.3                                                      
                   18.3                                                   
                      12.0                                                
                          7.4 660 11.5  200                               
D   56    9.4   52.1                                                      
                   22.8                                                   
                      16.0                                                
                          9.4 865 13.5  180                               
E   59    13.9  55.7                                                      
                   29.9                                                   
                      23.0                                                
                          14.1                                            
                              1050                                        
                                  15.5  190                               
__________________________________________________________________________
 
    
     
                                           TABLE 3                                 
__________________________________________________________________________
Variation of the activating temperature                                   
Lignite D                                                                 
Water content: 56% by weight                                              
Carbon charge: 375 g/h and onto dry carbon                                
             Benzene           Methylene                                  
Activating                                                                
       Furnace                                                            
             isotherm AS   Iodine                                         
                               blue  Molasses                             
temperature                                                               
       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;3000                                
700    27.2  14.3                                                         
                11.0                                                      
                    8.8                                                   
                        6.8                                               
                           295 0.5   &gt;3000                                
800    27.4  39.4                                                         
                17.3                                                      
                   12.2                                                   
                        8.0                                               
                           590 6.0   360                                  
850    24.5  39.7                                                         
                20.0                                                      
                   14.7                                                   
                        9.9                                               
                           670 6.0   370                                  
900    21.2  43.3                                                         
                20.8                                                      
                   15.3                                                   
                       10.1                                               
                           725 6.0   295                                  
950    12.1  52.9                                                         
                23.7                                                      
                   17.1                                                   
                       10.9                                               
                           835 9.0   215                                  
1000    6.0  58.8                                                         
                24.3                                                      
                   17.3                                                   
                       10.8                                               
                           790 10.5  170                                  
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                                           TABLE 4                                 
__________________________________________________________________________
Variation of the water content                                            
Lignite D                                                                 
Activating temperature: 950° C.                                    
Carbon charge: 300 g/h and onto dry carbon                                
Water      Benzene           Methylene                                    
Content                                                                   
     Furnace                                                              
           Isotherm AS   Iodine                                           
                             blue  Molasses                               
% by yield %                                                              
           (% by weight) value                                            
                             titer value                                  
weight                                                                    
     by 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   685                                    
16   27.8  23.8                                                           
              11.4                                                        
                  9.6                                                     
                     7.4 380 3.0   915                                    
20   29.5  30.4                                                           
              14.5                                                        
                 11.2                                                     
                     8.7 475 3.5   520                                    
26   25.4  35.0                                                           
              16.7                                                        
                 12.8                                                     
                     9.7 535 4.5   440                                    
32   17.9  44.5                                                           
              20.2                                                        
                 15.5                                                     
                     10.8                                                 
                         675 7.5   350                                    
46   16.5  48.8                                                           
              22.8                                                        
                 17.0                                                     
                     11.5                                                 
                         790 8.5   285                                    
56    9.4  52.1                                                           
              22.8                                                        
                 16.0                                                     
                     9.4 865 13.5  180                                    
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                                           TABLE 5                                 
__________________________________________________________________________
Influence of the addition of vapor                                        
Lignite D                                                                 
Activating temperature: 950° C.                                    
Water                                                                     
Content              Benzene           Methylene                          
of the    Addition                                                        
               Furnace                                                    
                     Isotherm AS   Iodine                                 
                                       blue  Molasses                     
lignite                                                                   
     Carbon                                                               
          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   335                          
56   300  --    9.4  52.1                                                 
                        22.8                                              
                           16.0                                           
                               9.4 865 13.5  180                          
56   900  --   26.9  29.5                                                 
                        17.8                                              
                           14.3                                           
                               10.2                                       
                                   610 4.0   965                          
56   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 catalysis                   
Activating temperature: 950° C.                                    
Carbon charge: 600 g/h and onto dry carbon                                
                     Benzene           Methylene                          
Potassium Water                                                           
               Furnace                                                    
                     Isotherm AS   Iodine                                 
                                       blue  Molasses                     
content % content                                                         
               yield %                                                    
                     (% by weight) value                                  
                                       titer value                        
Lignite                                                                   
    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  190                          
A   1.0   49.1 13.0  58.2                                                 
                        24.1                                              
                           14.5                                           
                                7.3                                       
                                   690 12.5  155                          
B   --    49.0 22.4  37.2                                                 
                        18.6                                              
                           12.7                                           
                                8.6                                       
                                   610  8.0  280                          
B   1.0   51.9 19.2  51.2                                                 
                        24.9                                              
                           17.5                                           
                               11.3                                       
                                   830 13.0  230                          
C   --    51.0 15.4  56.5                                                 
                        20.0                                              
                           13.3                                           
                                8.9                                       
                                   665 10.5  190                          
C   1.0   53.4 14.1  60.4                                                 
                        30.6                                              
                           20.8                                           
                               11.6                                       
                                   995 12.5  155                          
E   --    59.0 21.7  44.3                                                 
                        28.9                                              
                           23.4                                           
                               15.3                                       
                                   1035                                   
                                       13.0  415                          
E   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 content                                        
Lignite C                                                                 
Activating temperature: 950° C.                                    
Carbon charge: 600 g/h and onto dry carbon                                
                  Benzene           Methylene                             
       Water                                                              
            Furnace                                                       
                  Isotherm AS   Iodine                                    
                                    blue  Molasses                        
KOH 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  190                             
0.5    53.6 11.9  55.8                                                    
                     24.1                                                 
                        16.9                                              
                            10.8                                          
                                780 13.0  200                             
1.0    53.6 14.1  60.4                                                    
                     30.6                                                 
                        20.8                                              
                            11.6                                          
                                995 12.5  155                             
1.5    53.6 13.8  62.6                                                    
                     36.3                                                 
                        21.5                                              
                             9.4                                          
                                1200                                      
                                    18.0  150                             
2.0    53.6 14.1  60.9                                                    
                     38.1                                                 
                        22.3                                              
                            10.4                                          
                                1095                                      
                                    17.5  325                             
__________________________________________________________________________