Abstract:
A desulfurization process is described which consists of heating an organic hydrocarbon like coal or bitumen in a stream of a gaseous or liquid trapping material for hydrogen sulfide (H 2  S). The organic sulfur in the hydrocarbon decomposes and releases H 2  S which reacts with the trapping material to form a metastable sulfur compound. The resulting gaseous or liquid stream is recovered and decomposed in a subsequent step to form H 2  S and to the original trapping material. The trapping material is recovered and recirculated into the reactor. Ethylene, propylene and other olefins, as well as aldehydes and ketones are found to be excellent trapping materials.

Description:
BACKGROUND OF THE INVENTION 
     The state of the art of desulfurization of carbonaceous materials was reviewed by Attar in the 83rd Annual AICHE Meeting in Chicago, Ill. in November of 1980. (Copies of the paper are in the AICHE microfilm library.) The processes can be divided into the following categories: (1) desulfurization in oxidizing environment, e.g., the Arco, JPL, KVB, Ames and DOE processes, which use air, oxygen, chlorine or nitrogen oxide, to oxidize the coal and the sulfur compounds; (2) desulfurization processes using bases, e.g., the Battelle&#39;s Hydrothermal process or TRW&#39;s Gravimelt and Gravichem processes which use NaOH or Ca(OH) 2  in aqueous solutions; (3) desulfurization using hydropyrolysis, in which the coal is heated and pyrolyzed at a high temperature to produce desulfurizd char and hydrogen sulfide. Examples of such processes are Occidental&#39;s steam-hydrogen cyclic desulfurization process, IGT&#39;s hydrodesulfurization process and Illinois State Geological Survey&#39;s hydropyrolysis process; (4) miscellaneous other processes have been proposed including some which remove only pyritic sulfur, e.g., the Nedlog process which uses a magnetic field to separate iron pyrite, and several biodesulfurization processes. The proposed process is not related to any of the previously mentioned processes. 
     DESCRIPTION OF THE INVENTION 
     A two-step desulfurization process is used to remove sulfur from coal, tar sand, bitumen. The two steps consist of: 
     1. reacting the carbonaceous material with a compound which reacts with hydrogen sulfide (H 2  S), e.g., ethylene, propylene and other chemically similar compounds, herein referred to as the &#34;trapping material&#34;; 
     2. separating the sulfur containing reaction product and decomposing it to a stream of H 2  S and regenerated trapping material. 
     Contact times needed for reacting the trapping material with the carbonaceous material are generally under 20 minutes at the temperature range of 370°-430° C. for coals or at 180°-390° C. for bitumens. Application of pressures of 50-500 psi during the reaction enhances the sulfur removal rate, increases the desulfurization and allows treatment of larger particles. Reduction in the pressure and increasing the temperature allow catalytic and non-catalytic decomposition of the sulfurized trapping material to (1) H 2  S and (2) regenerated trapping material. The solid product of the reaction is coal, and not char. Therefore, it can be used in conventional pulverized fuel burners with no modifications of the burners. 
    
    
     FIG. 1 is a schematic diagram of one possible arrangement of the process units. The three major components are: 
     A. the desulfurization reactor, 
     B. the regeneration reactor, and 
     C. the H 2  S-separator. 
    
    
     Tables 1 and 2 describe the range of operating variables in the two reactors, assuming that the trapping material is ethylene and/or propylene. Separation of H 2  S from ethylene, propylene and from simlar materials is a well-established technology and will therefore not be discussed here. 
     Reactor B can be a catalytic plug flow or an empty tube reactor, depending on the trapping material used. 
     
                                           TABLE 1__________________________________________________________________________Range of Operation Variables in the DesulfurizationReactor (A)Temperature    Pressure  Particle Size                       Residence Time(°C.)    (psi)     (mesh)   (min.)    Preferred Preferred                  Preferred PreferredRange    Range    Range         Range              Range                  Range                       Range                            Range__________________________________________________________________________60-470    300-450    Vacuum-          80-200              1&#34; to                  1/4&#34; to                       1 sec. to                            3-30    coal 1000      -325                  -60  3 hr.                            min.60-300   100-600    bitumen   bitumen__________________________________________________________________________ 
    
     
                       TABLE 2______________________________________Range of Operation Variables in the RegenerationReactor* (B)Temperature  Pressure      Residence Time(°C.) (psi)         (min.)  Preferred          Preferred     PreferredRange  Range     Range    Range  Range  Range______________________________________250-700  450-550   Vacuum-  10-50  0.01 sec.-                                   0.1 sec-            100             20 min.                                   2 min.______________________________________ *Assuming no catalyst is used. 
    
     The sulfur compounds in carbonaceous materials decompose upon heating in reducing environment preferentially to hydrogen sulfide (H 2  S) and unsaturated compounds, e.g.: ##STR1## The H 2  S can react back with the solid matrix (where there is no trapping material) or with a trapping material. In the first case, no net desulfurization of the solid will be observed but in the second case, low sulfur solid will be produced once the sulfurized trapping material and the solid are separated. Typical trapping materials may be ethylene, propylene, other olefins, aldehydes, ketones, in liquid or gaseous form, or their mixtures which react reversibly with H 2  S. When the trapping material is ethylene, the reaction is: ##STR2## Application of increased pressure in the reactor enhances the rate of trapping, increases the equilibrium concentration of products like CH 3  CH 2  SH, and allows desulfurization of larger coal particles. 
     Once the resulting sulfurized trapping material is separated from the solid carbonaceous material, its pressure is reduced and its temperature increased. The sulfurized trapping material decomposes to H 2  S and to the original trapping material. An example of the reaction where ethylene is the trapping material is: ##STR3## Passing the gaseous mixture through a catalyst bed enhances the rate of decomposition of some sulfurized trapping materials. 
     Separation of the H 2  S from the regenerated trapping material can be accomplished by established technologies, e.g., distillation or absorption. 
     EXAMPLES 1-6 
     Several tests were conducted with a high sulfur Illinois #6 bituminous coal with and without a wash with dilute HCl. The characteristics of the raw material are described below: 
     
                       TABLE 3______________________________________The Ultimate Analysis and Sulfur Forms of the Coal of the______________________________________Study   Element  C      H     O    S     N    Ash______________________________________Unwashed   wt. %    70.44  5.08  9.96 3.52  1.30 9.7Washed  wt. %                                 8.8______________________________________    Sulfur Form               Total     Pyritic                               Sulfatic______________________________________Unwashed wt. %      3.52      0.35  0.42Washed   wt. %      3.10      0.35  0.007______________________________________ 
    
     The residence time of the bituminous coal in the reactor with the gaseous ethylene or N 2  according to the examples was 15 min at 410±5° C. at 100 psi. The flow rate of ethylene or N 2  was approximately 200 cm 3  /min and in the reactor there were 6 gms of -250 mesh coal. The sulfur forms in the coal products of the reaction are described in Table 4. The table also shows the total sulfur in the reacted coal after HCl wash. The data demonstrate clearly the effectiveness of C 2  H 4  as a trapping material for H 2  S and its effectiveness as a compound which reduces the recombination reaction of H 2  S with the solid matrix. 
     Mild pyrolysis of the coal appears to remove organic sulfur from coal and to convert some of the pyritic sulfur into iron sulfides. However, in the presence of calcium, i.e., when raw off mine coal is mildly pyrolyzed, no or little loss of sulfur is observed, since the sulfur released appears to react back with the basic minerals in the coal, according to the following reaction: 
     
         H.sub.2 S+CaO→CaS+H.sub.2 O 
    
     or: 
     
         H.sub.2 S+CaCO.sub.3 →CaS+H.sub.2 O+CO.sub.2 
    
     However, when a gaseous trapping material like C 2  H 4  is flowed through the reactor, it competes with the calcium minerals and sweeps the sulfur away from the reactor. Thus, a net desulfurization is observed. Since removal of the calcium can be accomplished only by expensive acid leaching and liquid solid separation processes, the use of a gaseous trapping material offers significant economic advantages over the addition of solid non-regenerable trapping materials. The results of examples 1 through 6 are: 
     
                       TABLE 4______________________________________Sulfur Forms in Reacted Coal                                      wt. %      wt.                        wt.  Tot S -      %      wt. %   wt. % wt. % %    HClSample     Ash    Sulfur  Sulfate                           Pyrite                                 FeS  washed______________________________________1   Raw coal    9.7   3.52  0.42  0.35  0.0  3.102   HCl-treated           8.8   3.10  0.01  0.35  0.0  3.103   Raw coal - 11.9   2.99  0.01  0.93   0.26                                        2.72    C.sub.2 H.sub.4 treated4   HCl-treated          10.5   2.44  0.01  0.09  0.0  2.43    C.sub.2 H.sub.4 treated5   Raw coal   12.2   3.26  0.01  0.50  0.0  3.25    N.sub.2 treated6   HCl-treated          10.7   2.47  0.01  1.06  0.0  2.46    N.sub.2 treated______________________________________ 
    
     EXAMPLES 7-9 
     A W. Kentucky bituminous coal with the properties described in Table 5 was treated with gaseous nitrogen or ethylene and/or propylene for 15 min. at 390°-410° C. in a fixed bed reactor with 200 cm 3  /min gas flow at 100 psi. The coal particles were -60+120 mesh. 
     
                       TABLE 5______________________________________Properties of a W. Ky Coal          Total    Sulfatic                           Pyritic                                  OrganicProperty  Ash     Sulfur   Sulfur  Sulfur Sulfur______________________________________wt. %  8.1     2.72     0.2     0.77   1.75______________________________________ 
    
     The following table illustrates the sulfur forms in the coal following the reaction: 
     
                       TABLE 6______________________________________Ash Content and Sulfur Forms in Reacted Coal         wt.                        % Total S         %      %       %     %     after HClExample  Gas    Ash    Total S Pyritic                              Sulfide                                    treatment______________________________________7      N.sub.2         8.7    2.3     0.5   0.2   2.18      C.sub.2 H.sub.4         8.9    0.95    0.4   0.3   0.659      C.sub.3 H.sub.6         8.9    1.05     0.45 0.3   0.75______________________________________ 
    
     An analysis of the organic sulfur functional group distribution in the ROM coal showed that over 2/3of the organic sulfur in this coal was thiolic or of the aliphatic sulfide structure. This is probably the reason why a large fraction of the organic sulfur was removed.