Abstract:
The present invention relates to a novel process for desulfurization of diesel with reduced hydrogen consumption. More particularly the subject invention pertains to an integrated process comprising diesel hydro de-sulfurisation (DHDS) or diesel hydrotreatment (DHDT) with reduced severity to desulfurize high sulfur (1.0-2.0 wt %) diesel stream to a much lower level of sulfur content of 350-500 ppm in the depleted diesel stream, followed by a novel adsorption procedure for effecting deep desulfurization to reduce overall sulfur content to less than 10 ppm with reduced hydrogen consumption, as compared to high severity DHDS or DHDT procedures of the prior art.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to desulfurization of diesel and in particular to a novel process for deep desulfurization of diesel with reduced hydrogen consumption. More particularly the subject invention pertains to an integrated process comprising diesel hydro de-sulfurisation (DHDS) or diesel hydrotreatment (DHDT) with reduced severity, to desulfurize high sulfur-containing (1-2%) diesel stream to a much lower level of sulfur content of 350-500 ppm in the treated diesel stream, followed by a novel adsorption procedure for effecting deep desulfurization to reduce overall sulfur content to less than 10 ppm with reduced hydrogen consumption, as compared to high severity DHDS or DHDT procedures followed in the prior art. 
       BACKGROUND OF THE INVENTION AND PRIOR ART 
       [0002]    With increasing concern for environmental pollution, regulatory norms are becoming increasingly stricter, forcing refiners to search for novel and economically viable routes to produce cleaner, eco-friendly fuels. The refining procedures adopted so far invariably use severe/drastic operating conditions involving high degree of hydrogen consumption and expensive catalyst systems. 
         [0003]    The residual sulfur below 500 ppm in diesel is mostly refractory sulfur. Removal of the refractory sulfur of the diesel through conventional hydrotreating requires severe operating conditions like higher pressure, lower ‘Liquid Hourly Space Velocity (LHSV)’, higher consumption of hydrogen, and use of highly active and expensive catalyst systems. 
         [0004]    The present invention provides a novel process to utilize a reactive adsorbent for reducing refractory sulfur present in diesel from 350-500 ppm to less than 10 ppm. The process developed in the present invention can be utilized in the downstream of existing DHDS/DHDT units. In the process, the hydrogen consumption is significantly low, since it is consumed only for saturation of olefinic bond generated by cleavage of the sulfur from the sulfur compounds. The combination will result in reduced hydrogen consumption at refineries. 
         [0005]    The DHDS procedure employs catalytic hydrogenation to upgrade the quality of diesel so as to conform to the environmental norms by mainly removing sulfur and nitrogen. In addition, this procedure brings about saturation of olefins and aromatic compounds. Catalysts are formulated by combining varying amounts of nickel or cobalt with molybdenum oxides on an aluminium base. Important operating parameters of this procedure are, inter alia, temperature, pressure, nature of catalyst, feed flow rate, feed characteristics, etc. The catalysts used therein are meant for carrying out reaction under less severe/drastic condition and at a faster rate. 
         [0006]    Removal of sulfur according to DHDS: Diesel contains sulfur compounds such as mercaptans, sulphides, and/or disulphides which are removed as H 2 S, as shown below: 
         [0000]      Mercaptan→C—C—C—C—SH+H 2 =C—C—C—C—H+H 2 S
 
         [0000]      Sulphide→C—C—S—C—C+2H 2 =2C—C—H+H 2 S
 
         [0000]      Disulphide→C—C—S—S—C—C+3H 2 =2C—C—H+2H 2 S
 
         [0007]    US publication US20070261994A1 discloses a method for producing a super-low sulfur gas oil blending component or a super-low sulfur gas oil composition having a sulfur content of less than 5 ppm, under relatively mild conditions, without greatly increasing the hydrogen consumption and without remarkably decreasing the aromatic content. However unlike the present invention, the hydrogen consumption reduction is not clearly specified. Moreover the composition of the catalyst used is different. The present invention uses a process of splitting the treated diesel between two fractions, which is not present in this US publication. 
         [0008]    U.S. Pat. No. 6,551,501B1 discloses a combined process for improved hydrotreating of diesel fuels, in which the feed to be hydrotreated is pretreated with a selective adsorbent prior to the hydrotreating step to remove polar materials, especially nitrogen containing compounds (N-compounds). In the present invention both the hydrotreatment and adsorption process are used to reduce the sulfur content in the fuel; however, the reduction of sulfur content in two publications is different. In the US publication the splitting of hydrocarbon and reduction of hydrogen consumption is not mentioned. 
         [0009]    PCT application WO2008122706A2 discloses an improved method for deep desulphurisation of a gasoil comprising a catalytic hyrodesulphurisation unit preceded by an absorption unit for nitrogen compounds inhibiting the hydrodesulphurisation reaction. However, the present invention uses either DHDT or DHDS process followed by adsorption process for sulfur removal. The type of catalyst, reduction of hydrogen consumption and reduction of severity are not mentioned in the PCT publication. 
         [0010]    US publication US2007023325A1, by the applicant of the present invention has been mentioned separately in the following description. It discloses the adsorbent that has been used in the present invention too. 
         [0011]    Hence there is a need to provide such a desulfurization process that the sulfur content of the diesel can be brought down to less than 10 ppm, while ensuring minimum consumption of hydrogen. This invention therefore aims at overcoming the difficulties or drawbacks of the procedures adopted in the prior art for desulfurization of diesel. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides an integrated process for deep desulfurization of diesel. The integrated process comprises of DHDS or DHDT process which operates with reduced severity and a novel reactive adsorption process. While the DHDS or the DHDT process reduces the sulfur content of the diesel being treated to 350-500 ppm, the adsorption process further reduces the sulfur content to &lt;10 ppm. 
         [0013]    The present invention further provides splitting of treated diesel containing about 350 ppm of refractory sulfur into two cuts viz Initial boiling point (IBP) 140-150° C.-280/300° C. and Final boiling point (FISP) 280/300° C. The 280/300° C.-IBP cut contains preferably less than 20 ppm sulfur and more preferably less than 10 ppm sulfur which can be blended into diesel stream without any further treatment and the 280/300° C.-FBP cut containing about 500-600 ppm of refractory sulfur can be desulfurized using novel adsorption process capable of bringing down sulfur content of diesel to less than 10 ppm. 
         [0014]    Accordingly, the process in accordance with this invention can be utilized in the downstream of existing DHDS/DHDT units. The present invention shows consumption of hydrogen is significantly low as compared to the prior art, because hydrogen is consumed only for bringing about saturation of olefinic bonds generated by cleavage of sulfur from the sulfur-containing compounds. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention discloses a novel process for desulfurization of diesel with reduced hydrogen consumption, which comprises hydrotreating high sulfur-containing diesel stream (1.0-2.0% by wt. of 5) over a NiMo catalyst to reduce sulfur-content to a level of 350-500 ppm, followed by subjecting the treated diesel stream to a novel adsorption procedure to bring down sulfur content to less than 10 ppm. 
         [0016]    In this integrated process, high sulfur diesel stream containing about 1.0-2.0 wt % sulfur can be hydrodesulfurized to a level of 350-500 ppm sulfur product utilizing conventional DHDS or DHDT process with subsequent processing by novel adsorption process to reduce sulfur content below 10 ppm. 
         [0017]    In one embodiment, the present invention, treated diesel containing about 350 ppm of refractory sulfur is split into two cuts viz. IBP(140-150° C.)-280/300° C. and FBP 280/300° C. The280/300° C.-IBP cut contains preferably less than 20 ppm sulfur and preferably less than 10 ppm sulfur. This cut can be blended into diesel stream without any further treatment. The 280/300° C.-FBP cut containing about 500-600 ppm of refractory sulfur can be desulfurized using novel adsorption process. 
         [0018]    The adsorption process comprises two numbers of fixed bed reactors, which are being operated in swing mode of adsorption and regeneration. During the adsorption process, 280/300° C.-FBP cut along with hydrogen is contacted with the adsorbent in down or up flow mode at 350-400° C., 15-30 bar, hydrogen to hydrocarbon ratio of 100-400 Nm 3 /m 3 , liquid hourly space velocity of 0.5-2.0 h −1  depending on the sulfur contents of feed. During the adsorption process, the sulfur compounds are chemically adsorbed on the adsorbent followed by cleavage of the sulfur atom form the sulfur compound. The hydrocarbon molecule of the sulfur compound is released back into the hydrocarbon stream. The presence of hydrogen during the adsorption also prevents deactivation of adsorbent due to coking. The treated diesel contains less than 10 ppm sulfur which can be blended with other cut to produce diesel pool containing less than 10 ppm sulfur. After reaching the breakthrough point, the adsorbent is regenerated at 350-500° C. 
         [0019]    Regeneration of adsorbent is accomplished in situ by controlled oxidation of the adsorbed carbon and sulfur with lean air followed by activation with hydrogen. The cycle time will vary from 4 to 10 days depending on feed sulfur and boiling range. The adsorbent has higher strength and thermal stability compared to hydrotreating catalyst. The regenerability study for the adsorbent has been conducted in pilot plant for 6 months ( 25 cycles) and there was no loss of activity and physical properties, hence the life of the adsorbent is expected to be similar to that of hydrotreating catalyst systems.    
         [0020]    Adsorbent: The adsorbent used in the process is disclosed in prior art (US 2007/0023325) which is comprised of a base component, a reactive component, and booster. The base component of adsorbent is a porous material, which provides extrudibility and strength. Such materials include alumina, clay, magnesia, titania or a mixture of two or more such materials. The reactive component of the adsorbent is a spinel oxide and prepared through solid-state reaction of the individual metal oxides. This component is responsible for detaching the sulfur atom from the sulfur compounds. The activity booster component of the adsorbent is a bimetallic alloy generated in situ from mixed metal oxides. 
         [0021]    The present invention also provides a process for regeneration of adsorbent comprises the steps of controlled oxidation of the adsorbed carbon and sulfur with lean air at a temperature ranging between 350° C. and 500° C., and activation with hydrogen wherein the process is carried out in situ. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION ACCOMPANYING DRAWINGS 
         [0022]    The present invention will be further explained with the help of the drawings accompanying this specification, in which 
           [0023]      FIG. 1  shows a flow diagram of hydroprocessing micro reactor unit (MRU); 
           [0024]      FIG. 2  shows GC-SCD chromatograms of 350 and 10 ppm sulfur-product diesel; 
           [0025]      FIG. 3  depicts the integrated process scheme for deep desulfurization of high sulfur diesel feedstock and 
           [0026]      FIG. 4  gives a schematic representation of the novel adsorption procedure. 
       
    
    
       [0027]    The invention will be further defined by the examples given hereafter by way of illustration and not by way of limitation. 
       EXAMPLES 
     Example-1 
       [0028]    Diesel stream containing 1.53 wt % sulfur was hydrodesulfurized using commercial DHDS and DHDT catalyst system in a hydroprocessing micro-reactor unit (MRU). The process flow diagram of MRU is shown in  FIG. 1 . The severity of operating parameters was chosen to get 10-30 ppm sulfur product. The details of feed/ product properties and operating conditions are given in Table-1: 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Details of feed/product properties and operating conditions 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. Operating Conditions 
                   
                 DHDT 
                 DHDS 
               
               
                   
               
               
                 LHSV, h −1   
                   
                 0.6 
                 0.6 
               
               
                 Temperature, ° C. 
                   
                 370 
                 370 
               
               
                 H 2 /HC ratio, Nm 3 /m 3   
                   
                 400 
                 400 
               
               
                 Pressure, bar 
                   
                 100 
                 50 
               
               
                 2. Catalyst 
                   
                 NiMo 
                 CoMo 
               
               
                   
               
               
                 3. Feed/product 
                   
                 DHDT 
                 DHDS 
               
               
                 properties 
                 Feed 
                 Product 
                 Product 
               
               
                   
               
               
                 a) Density @ 
                 0.8449 
                 0.8107 
                 0.8265 
               
               
                 15° C., g/cc 
               
               
                 b) Sulfur, ppm 
                 15300 
                 20 
                 30 
               
               
                 c) CI (D4737) 
                 50.8 
                 57.9 
                 55.1 
               
               
                 4. H 2  Consumption, 
                   
                 1.3 
                 1.0 
               
               
                 wt % of feed 
               
               
                   
               
             
          
         
       
     
       EXAMPLE-2 
       [0029]    Diesel stream containing 1.53 wt % sulfur was hydrodesulfurized using highly active commercial DHDS and DHDT catalyst system in a hydroprocessing micro-reactor unit (MRU). The severity of operating parameters was reduced to get 350 ppm sulfur product. The details of feed/ product properties and operating conditions are given in Table-2: 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Details of feed/product properties and operating 
               
               
                 conditions (350 ppm sulfur product) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. Operating Conditions 
                   
                 DHDT 
                 DHDS 
               
               
                   
               
               
                 LHSV, h −1   
                   
                 1.0 
                 1.0 
               
               
                 Temperature, ° C. 
                   
                 350 
                 350 
               
               
                 H2/HC, Nm 3 /m 3   
                   
                 250 
                 250 
               
               
                 Pressure, bar 
                   
                 50 
                 50 
               
               
                 2. Catalyst 
                   
                 NiMo 
                 CoMo 
               
               
                   
               
               
                 3. Feed/product 
                   
                 DHDT 
                 DHDS 
               
               
                 properties 
                 Feed 
                 Product 
                 Product 
               
               
                   
               
               
                 a) Density @ 15° C., g/cc 
                 0.8449 
                 0.8279 
                 0.8283 
               
               
                 b) Sulfur, ppm 
                 15300 
                 350 
                 350 
               
               
                 c) CI (D4737) 
                 50.8 
                 54.5 
                 54.2 
               
               
                 4. H2 Consumption, 
                   
                 0.7 
                 0.7 
               
               
                 wt % of feed 
               
               
                   
               
             
          
         
       
     
         [0030]    The 350 ppm sulfur product was subsequently treated by novel adsorption process to reduce total sulfur content below 10 ppm. The detailed GC-SCD analysis of 350 and 10 ppm sulfur product diesel is given below in Table-3. The GC-SCD Chromatograms of 350 and 10 ppm sulfur product diesel is given below in  FIG. 2  of the drawings. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 GC-SCD of 350 and 10 ppm sulfur Product Diesel 
               
             
          
           
               
                   
                 Total ‘S’ in ppm 
               
             
          
           
               
                   
                   
                 RT 
                 350 ppm ‘S’ 
                 &lt;10 ppm ‘S 
               
               
                 S. No. 
                 ‘S’ Compound 
                 Minutes 
                 Product 
                 Product 
               
               
                   
               
             
          
           
               
                 1 
                 C6BT-4 
                 38.73 
                 4 
                   
               
               
                 2 
                 C7BT-1 
                 41.15 
                 5 
               
               
                 3 
                 4-MDBT 
                 41.68 
                 27 
               
               
                 4 
                 MDBT-1 
                 42.19 
                 5 
               
               
                 5 
                 MDBT-2 
                 42.55 
                 6 
               
               
                 6 
                 C7BT-2 
                 42.85 
                 8 
               
               
                 7 
                 C2DBT-1 
                 44.13 
                 8 
               
               
                 8 
                 4,6-DMDBT 
                 44.44 
                 35 
                 2.0 
               
               
                 9 
                 C2DBT-2 
                 44.99 
                 32 
               
               
                 10 
                 C2DBT-3 
                 45.66 
                 24 
               
               
                 11 
                 C2DBT-4 
                 46.05 
                 17 
               
               
                 12 
                 C2DBT-5 
                 46.44 
                 3 
               
               
                 13 
                 C2DBT-6 
                 46.67 
                 17 
                 0.7 
               
               
                 14 
                 C3DBT-1 
                 47.37 
                 24 
               
               
                 15 
                 C3DBT-2 
                 47.90 
                 12 
               
               
                 16 
                 C3DBT-3 
                 48.27 
                 16 
                 0.6 
               
               
                 17 
                 C3DBT-4 
                 48.67 
                 26 
                 0.3 
               
               
                 18 
                 C3DBT-5 
                 49.08 
                 7 
               
               
                 19 
                 C3DBT-6 
                 49.26 
                 3 
               
               
                 20 
                 C3DBT-7 
                 49.52 
                 9 
               
               
                 21 
                 C4DBT-1 
                 49.78 
                 7 
               
               
                 22 
                 C4DBT-2 
                 50.27 
                 11 
               
               
                 23 
                 C4DBT-3 
                 50.67 
                 10 
                 0.4 
               
               
                 24 
                 C4DBT-4 
                 51.20 
                 16 
               
               
                 25 
                 C4DBT-5 
                 51.90 
                 3 
               
               
                 26 
                 C4DBT 
                 52.17 
                 9 
               
               
                 27 
                 C5DBT-1 
                 52.52 
                 5 
               
               
                 28 
                 C5DBT-2 
                 52.83 
                 3 
                   
               
               
                   
                   
                 Total 
                 350 
                 4 
               
               
                   
               
             
          
         
       
     
         [0031]    It may be observed from GC-SCD of 350 ppm residual sulfur containing diesel, the most of the sulfur compound exist in the boiling above 300° C. 
       EXAMPLE-3 
       [0032]    Since most of the sulfur compounds exist in the boiling range above 300° C. in 350-500 ppm hydrodesulfurized diesel (example-2), the 350 ppm sulfur product diesel from DHDS or DHDT was split into two cuts viz. IBP to 280° C. and FBP to 280° C. The 280° C. IBP cut contains less than 10 ppm sulfur. The 280° C.-FBP cut containing 530 ppm of refractory sulfur was desulfurized using novel adsorption process to reduce sulfur below 10 ppm. The details of various cuts and final product diesel are given below in Table-4. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Details of various cuts and final product diesel 
               
             
          
           
               
                   
                   
                   
                 280° C. -FBP 
                 Final 
               
               
                   
                 IBP-280° 
                 280° C. -FBP 
                 treated by 
                 Product 
               
               
                 Property 
                 C. 
                 (390° C.) 
                 Adsorption process 
                 Diesel 
               
               
                   
               
             
          
           
               
                 Wt fraction 
                 0.35 
                 0.65 
                 0.65 
                 1.00 
               
               
                 S, ppm 
                 8 
                 530 
                 6 
                 7 
               
               
                 Density, g/cc 
                 0.83 
                 0.8450 
                 0.8450 
                 0.8397 
               
               
                   
               
             
          
         
       
     
         [0033]    The integrated process scheme for deep desulfurization of high sulfur diesel feed stocks is given in  FIG. 3 . 
         [0034]    In this process scheme shown in  FIG. 3  of the drawings, the liquid product from the separator of DHDS/DHDT is sent to splitter where wild naphtha [150 (−)° C. cut] is separated from top of the column, 150-280° C. cut from the middle and 280(+)° C. cut from bottom is separated. Bottom or bottom along with middle cut further deep desulfurized using novel adsorption process to reduce total sulfur content below 10 ppm. The Adsorption process scheme is given in  FIG. 4  of the drawings. 
         [0035]    In the Adsorption process cetane number of the product is not improved. However, since cetane number specification is same for Euro-III and Euro-IV diesel, the process is particularly suitable as a finishing step for further treatment of Euro-III diesel after DHDS/DHDT. 
         [0036]    The existing DHDT unit can be operated at lesser severity, just sufficient to meet the cetane requirement, and further sulfur reduction can be achieved by employing the novel adsorption process. This will result in substantial saving of precious hydrogen. From the data (Table-5), it can be observed that by combining novel adsorption process with DHDS or DHDT units saves about 20 to 40% hydrogen consumption respectively. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Saving of hydrogen by integration of Adsorption 
               
               
                 process with DHDS or DHDT unit 
               
             
          
           
               
                   
                   
                 Hydrogen Consumption 
               
               
                 S. No. 
                 Activity 
                 wt % of feed 
               
               
                   
               
             
          
           
               
                 1. 
                 From 1.53% sulfur feed 
                 1.0 
               
               
                   
                 to 30 ppm sulfur 
               
               
                   
                 product by DHDS (CoMo) 
               
               
                   
                 From 1.53% sulfur feed 
                 0.70 
               
               
                   
                 to 350 ppm sulfur 
               
               
                   
                 product by DHDS (CoMo) 
               
               
                   
                 From 350 ppm sulfur 
                 0.1 
               
               
                   
                 product to &lt;10 ppm 
               
               
                   
                 sulfur product by 
               
               
                   
                 Adsorption process 
               
               
                   
                 Saving of hydrogen as 
                 0.20 
               
               
                   
                 per present invention 
               
               
                   
                 DHDS vs. DHDS + 
               
               
                   
                 Adsorption process 
               
               
                 2. 
                 From 1.53% sulfur feed 
                 1.30 
               
               
                   
                 to 20 ppm sulfur 
               
               
                   
                 product by DHDT (NiMo) 
               
               
                   
                 From 1.53% sulfur feed 
                 0.70 
               
               
                   
                 to 350 ppm sulfur 
               
               
                   
                 product by DHDT (NiMo) 
               
               
                   
                 From 350 sulfur 
                 0.10 
               
               
                   
                 product to &lt;10 sulfur 
               
               
                   
                 product by Adsorption 
               
               
                   
                 process 
               
               
                   
                 Saving of hydrogen as 
                 0.50 
               
               
                   
                 per present invention 
               
               
                   
                 DHDT vs. DHDT + 
               
               
                   
                 Adsorption process 
               
               
                   
               
             
          
         
       
     
       Advantages of the Present Invention 
       [0000]    
       
         
           
             i. The invention offers an integrated process comprising DHDS or DHDT operating with reduced severity followed by novel reactive adsorption process. 
             ii. The deep desulfurization procedure involving high sulfur-containing diesel stream effectively brings down the sulfur content to less than 10 ppm. 
             iii. The invented process reduces hydrogen consumption by 20-40% as compared to only DHDS or DHDT procedure with high severity. 
             iv. The subject invention effectively reduces severity of DHDS or DHDT procedure and brings down sulfur content to 350-500 ppm level, with a further reduction to less than 10 ppm by employing the novel reactive adsorption procedure. 
           
         
       
     
         [0041]    Although, the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the invention as recited in the accompanying claims.