Abstract:
The present invention describes a process for regenerative reforming of gasolines, characterized by recycling at least a portion of the effluent from the catalyst reduction zone to the inlet to the feed/effluent exchanger that can pre-heat the feed, the other portion possibly being recycled to the head of the first reactor, and by recycling gas from the recycle compressor to the head of the penultimate reactor of the series. This disposition can significantly improve the production of reformate and the hydrogen balances of the unit.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to the field of catalytic reforming of gasolines, and more generally to moving bed processes. More specifically, it is applicable to regenerative reforming or to the production of BTX (benzene, toluene, xylenes) with continuous catalyst regeneration. 
         [0002]    The process for the catalytic reforming of gasolines employing a reaction zone comprising a series of 3 or 4 reactors in series, operating in moving bed mode, and has a catalyst regeneration zone which itself comprises a certain number of steps, including a step for combustion of coke deposited on the catalyst in the reaction zone, an oxychlorination step, and a final step for reduction of catalyst in hydrogen. After the regeneration zone, the catalyst is re-introduced to the head of the first reactor of the reaction zone. 
         [0003]    More precisely, the invention concerns a novel process for catalytic reforming of gasolines comprising a recycle of effluent from the catalyst reduction step upstream of the first reactor of the reaction zone and injection of recycled hydrogen to the last or penultimate reactor in order to maintain a partial pressure of hydrogen which is higher on said last reactors and thus to limit deactivation of the catalyst at the end of the reaction zone. 
         [0004]    This novel disposition has a number of advantages:
       it reduces or even eliminates the re-introduction of water into the reaction system;   it encourages the reactions of naphthene dehydrogenation and dehydrocyclization of paraffins contained in the feed, i.e. those occurring in the first two reactors due to a reduction in the partial pressure of hydrogen in those two reactors, a reduction which is thermodynamically favourable to the reactions in question;   it also favourably modifies the distribution of hydrogen between the various reactors by increasing the H 2 /HC ratio on the last or last two reactors which are precisely those in which coke has a preferential tendency to form.       
 
       EXAMINATION OF THE PRIOR ART 
       [0008]    According to the prior art, the reduction effluent from a catalytic reforming unit is generally sent either to the intake of the re-contacting compressor of the hydrogen purification section or to the “fuel gas” grid of the refinery, i.e. to the grid for the gas used as a fuel in the various units or furnaces of the refinery. 
         [0009]    The reduction effluent may also be sent in its entirety or in part to the inlet to the separator drum in order to adjust the quantity of water in the recycle gas. 
         [0010]    The flowcharts for the prior art purification zone are not modified by the present invention which essentially concerns the reaction zone. 
         [0011]    Patent FR 2 801 604 describes a process for the production of aromatics using a catalyst moving in a moving bed, which process comprises at least two steps characterized by a certain (H 2 )/(HC) ratio, H 2  representing the quantity of hydrogen introduced into said step and HC representing the quantity of feed entering said step. 
         [0012]    In the patent cited above, the catalyst reduction step is also characterized by certain values for the ratio H 2 /HC. The values for the H 2 /HC ratios for the two reaction steps and that of the catalyst reduction step are linked by an inequality. However, in all cases, the recycled hydrogen is sent to the first reactor of the reaction section and thus does not result in favouring the reactions sought in this process which are essentially the reactions of dehydrogenation of naphthenes or the dehydrocyclization of paraffins greatly favoured by low partial pressures of hydrogen. 
         [0013]    Patent FR 2 801 605 describes a process for the production of aromatics using a moving bed catalyst which comprises a step for reduction of said catalyst in the presence of a recycle gas introduced in a quantity such that the quantity of pure hydrogen supplied to the catalyst reduction step is in the range 1 to 10 kg/kg of catalyst. 
         [0014]    Patent application FR 09/02802 describes a circuit for recycling effluent from the reduction zone to the last reactor or reactors of the reaction zone. This recycle does not modify the partial pressure of hydrogen in the first reactor, which is precisely the action sought in the present application. 
         [0015]    None of those three documents, which may be considered to represent the closest prior art, discloses in a precise manner the re-introduction of effluent derived from the catalyst reduction step to the head of the first reactor and/or the injection of effluent derived from the separator drum of the recycle compressor (RCY), generally known as the recycle gas, to the head of the last or penultimate reactor of the reaction zone of a catalytic gasoline reforming unit. The combination of these two streams results in an improvement in the unit yields, in particular as regards the reformate defined as hydrocarbons containing more than 4 carbon atoms and denoted C4+. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0016]      FIG. 1  represents a general view of a catalytic reforming unit comprising 4 reactors in series and a catalyst regeneration zone. 
       
    
    
       [0017]    The catalyst circuit is marked in thicker lines. 
         [0018]      FIG. 1  shows the recycle of the reduction effluent  4  in part to the head of the first reactor and in part to the inlet to the feed/effluent exchanger as well as the re-introduction of recycle gas  7  from the recycle compressor RCY to the head of the last (R 4 ) and penultimate (R 3 ) reactor. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0019]    The present invention may be defined as a process for catalytic reforming of a gasoline with a distillation range in the range 60° C. to 250° C. employing a moving bed catalytic reforming unit comprising at least four reactors in series, and a regeneration zone for said catalyst, in which the effluent from the catalyst reduction step forming part of the catalyst regeneration zone is recycled in part to the inlet to the feed/effluent exchanger E 1 , with the other portion being recycled to the head of the first reactor R 1  and in which the gas stream derived from the recycle compressor RCY is sent to the head of the penultimate reactor R 3  of the reaction section. 
         [0020]    In accordance with a first variation of the present invention, the gaseous effluent from the reduction step is sent in its entirety to the inlet to the feed/effluent exchanger. 
         [0021]    In accordance with a second variation of the present invention, the gaseous effluent from the reduction step is sent in its entirety to the head of the first reactor. 
         [0022]    In accordance with a third variation of the invention, the gaseous stream derived from the recycle compressor RCY is sent in its entirety to the head of the third reactor. 
         [0023]    A variation which combines any one of variations 1 and 2, concerning the gaseous reduction effluent, with variation 3 which concerns the gaseous stream deriving from the recycle compressor RCY, for example variation 1 and variation 3, or variation 2 and variation 3, fall within the scope of the invention. 
         [0024]    More precisely, in a first configuration of the process for catalytic reforming of a gasoline in accordance with the present invention, the gaseous reduction effluent  4  is sent in its entirety to the head of the first reactor R 1 , and the effluent  7  from the recycle compressor RCY is sent in its entirety to the penultimate reactor R 3 . 
         [0025]    In a second configuration of the process for catalytic reforming of a gasoline in accordance with the present invention, the gaseous reduction effluent  4  is sent in its entirety to the inlet to the feed/effluent exchanger E 1 , and the effluent  7  from the recycle compressor RCY is sent in its entirety to the penultimate reactor R 3 . 
         [0026]    Several technical advantages result from sending a portion of the reduction effluent to the inlet to the feed/effluent exchanger and a portion to the head of the first reactor. 
         [0027]    Firstly, the reduction in the partial pressure of hydrogen in the first reactor results in a substantial increase in the production of aromatics and hydrogen with respect to the conventional prior art layout. In fact, the reduction in the H 2 /HC ratio on reactor R 1  can improve the naphthene dehydrogenation reactions in said reactors and reduce cracking of long chain paraffins. 
         [0028]    Further, the reduction in the partial pressure of hydrogen on the first reactor R 1  results in a reduction in the consumption of the recycle compressor RCY and finally in a reduction in the size of said compressor because of the new discharge pressure thereof and/or in the reduction in the recycle ratio. The discharge pressure of the recycle compressor RCY is in fact substantially reduced compared with the prior art. Said discharge pressure is substantially equal to the inlet pressure of the first reactor in the prior art and equal to the pressure of the last or penultimate reactor for the process of the invention. 
         [0029]    Further, recycling the effluent from the recycle compressor RCY arriving at the head of the last (R 4 ) or penultimate (R 3 ) reactor means that the H 2 /HC ratio in these reactors in which the major portion of the coke is produced can be substantially increased. 
         [0030]    This increase in the H 2 /HC ratio on the last reactors R 3  or R 4  can either reduce the coke to be regenerated or, for the same quantity of coke, can reduce the flow rate of recycle gas on the last (R 4 ) or the penultimate (R 3 ) reactor. Thus, a substantial saving in consumption is obtained for the recycle compressor RCY. Regarding the technology of the reaction section, two cases are possible:
       the reactors R 1 , R 2 , R 3 , R 4  are disposed side by side, the catalyst being transported from the bottom of one reactor (Rp) to the head of the next reactor (Rp+1) then arriving at the last reactor and being supplied to the regeneration column via a lift line;   the reactors R 1 , R 2 , R 3 , R 4  are disposed in a vertical stack and the catalyst then flows under gravity from one reactor (Rp) to the next (Rp+1) located below Rp. A lift line at the bottom of the last reactor can introduce catalyst to the head of the regeneration column.       
 
         [0033]    The present invention is perfectly compatible with the two technologies, one being termed “side by side” and the other, “stacked”. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    The detailed description below is made with reference to  FIG. 1 . 
         [0035]    A catalytic reforming unit for gasolines (distillation range 60° C. to 250° C.) comprises a reaction section constituted by at least four reactors denoted R 1 , R 2 , R 3 , R 4  (or even R 5 ) operating in series, and a catalyst regeneration zone comprising a step I for combustion of coke deposited on the catalyst, a step II for oxychlorination in order to re-disperse the crystallites, and a step III for reduction in hydrogen which can reduce oxides of the catalyst before re-introducing it into the reaction zone. 
         [0036]    The reaction zone is constituted by 4 reactors denoted R 1 , R 2 , R 3 , R 4  represented in  FIG. 1  in the “side by side” configuration. 
         [0037]    The feed to be treated  1  passes through the feed/effluent exchanger E 1  then the pre-heating furnace F 1  before being introduced into the first reactor R 1  of the series (stream  3 ). 
         [0038]    The catalyst moves in the various reactors of the reaction zone as a moving bed and is traversed substantially radially by the feed to be treated  3  and the various intermediate effluents  8  at the inlet of R 2 ,  9  at the inlet to R 3  and  10  at the inlet to R 4 . 
         [0039]    The reaction effluent at the outlet from reactor R 4  is cooled in the feed/effluent exchanger E 1  then in an air-cooled exchanger and an exchanger before being sent to the separator drum BS from which the gas termed the “recycle gas” is extracted overhead and sent to the recycle compressor RCY, and a stream of molecules containing more than 4 carbon atoms (denoted C4+) which constitutes the reformate is withdrawn from the bottom. 
         [0040]    The catalyst is then regenerated in the regeneration zone which comprises a step for combustion of coke deposited on the catalyst I, an oxychlorination step II and a hydrogen reduction step III. 
         [0041]    The whole of the regeneration zone has not been shown in  FIG. 1 . All that is shown is the last step for catalyst reduction (denoted RED) employing a hydrogen-rich gas (stream  4 ′). This stream  4 ′ is much richer in hydrogen (more than 90% molar) than the recycle gas  7  (hydrogen content 80% to 87% molar). 
         [0042]    The catalyst regenerated at the outlet from the reduction step RED is re-introduced to the head of the first reactor R 1 . 
         [0043]    The step for reduction of the catalyst supplied by a hydrogen-rich stream  4 ′ deriving from the high pressure re contacting drum (not shown in  FIG. 1 ) or derived from the purification of hydrogen (as in PSA processes or any other process known to the skilled person) generates a reduction gas which is termed the reduction effluent  4  in the remainder of the text. In the prior art, this reduction effluent  4  is re-introduced upstream of the recycle compressor (denoted RCY) or upstream of the separator drum (denoted BS). 
         [0044]    In the present invention, this reduction effluent  4  is recycled in part to the head of the first reactor R 1  via the stream  6  and in part to the inlet to the feed/effluent exchanger E 1  via the stream  5 . 
         [0045]    In a particular case of the present invention, the reduction effluent  4  is recycled in its entirety to the inlet to the feed/effluent exchanger E 1 . 
         [0046]    Finally, a portion of the effluent  7  derived from the recycle compressor, termed the recycle gas, is sent in part to the head of the last reactor R 4  (stream  7   b ) and in part to the head of the penultimate reactor R 3  of the reaction zone (stream  7   a ). 
         [0047]    In a preferred variation of the present invention, the effluent  7  derived from the recycle compressor RCY is sent in its entirety to the head of the penultimate reactor R 3  (stream  7   a ). 
         [0048]    A variation of the invention uses the concept of parallel or hybrid circulation as described in the Applicant&#39;s patent U.S. Pat. No. 7,285,205. That type of circulation is also valid for the two proposed arrangements of the reactors, i.e. the “side by side” or “stacked” configurations. 
         [0049]    The hydrogen leaving the reduction step RED, termed the reduction effluent  4 , generally has the following characteristics:
       Pressure: 5.2 bars effective (1 bar=10 5  pascals) plus or minus 0.5 bar;   Temperature: 450° C.-520° C.;   Hydrogen content: 90% to 99.9% by volume;   Chlorine content: 20-50 ppm by volume;   Water content: 50-100 ppm by volume;   First reactor inlet pressure: 4.9 bar effective.       
 
       EXAMPLES 
       [0056]    Two examples will be compared, one in accordance with the prior art and the other in accordance with the invention. The example of the invention does not in any case limit the operating conditions of the present invention. It merely serves to provide a measure of the advantages arising from the present invention compared with the prior art example. 
         [0057]    The common operating conditions of the prior art example and the example of the invention were as follows: 
         [0058]    Feed:
       Feed flow rate: 75 tonnes/hour;   Distillation range: 60° C. to 250° C.;   PNA (vol %): 53/41/6;   Motor octane number: 102       
 
         [0063]    Operating Conditions:
       Hourly space velocity: 2 h −1 ;   Recycle ratio: molar flow rate of H 2 , 7, deriving from recycle compressor RCY/molar flow rate of fresh HC feed  1 :
           equal to 1.5 and sent to R 1 , according to prior art;   equal to 1.5 and sent to R 3 , according to invention;   
           Reactor inlet temperature for R 1 , R 2 , R 3 , R 4 : 515° C.       
 
         [0069]    a) In accordance with the prior art, the recycle gas derived from the low pressure separator drum BS was sent upstream of the feed/effluent exchanger which preceded the first reactor R 1 . The H 2 /HC ratio sent to reactor R 1  was 1.5 (mole/mole). 
         [0070]    b) In accordance with the present invention, in one of its configurations, the recycle gas derived from the separator drum BS was sent to the inlet to the penultimate reactor R 3  (stream  7   a ) and the reduction effluent was sent to the head of the first reactor R 1  (stream  6 ). 
         [0071]    The H 2 /HC ratio sent to the reactor R 3  was 1.5 (mole/mole). 
         [0072]    This resulted in a completely different pressure balance at the recycle compressor RCY.
       in accordance with the prior art: the pressure differential due to the pressure drops of the circuit and the various constituent elements (furnaces, reactors, lines, exchangers, control instrument) was 3.5 bar between the intake and discharge. The compressor had a consumption of 3620 kW;   in accordance with the invention: the pressure differential is only 1.9 bar, which greatly limited the dimensions and the consumption of the recycle compressor RCY. The compression ratio of the recycle compressor RCY thus changed from 2.1 in accordance with the prior art to 1.6 in accordance with the invention.       
 
         [0075]    The consumption of the compressor was 2250 kW, i.e. a reduction of practically 40% with respect to the prior art.
       1) The recycle of the reduction effluent (stream  6 ) to the head of the first reactor R 1  allowed chlorinated compounds on the catalyst present in reactors R 1  or R 2  to be re-adsorbed. This effect of re-adsorption of chlorinated compounds also meant that there was a reduction of approximately 30% in the consumption of chlorine in the catalyst regeneration loop.   2) Recycling the reduction effluent (stream  6 ) to the head of R 1  also meant that the selectivity of the catalyst was substantially improved since the yield of C5+ cut changed from 90.1% in the prior art to 91.3% in the invention.   3) Finally, recycling the reduction effluent (stream  6 ) to the head of reactor R 1  meant that injection of water into the feed could be reduced (or in some cases dispensed with entirely). In the present case, this injection was reduced from 4 ppm by weight to 1.4 ppm by weight.       
 
         [0079]    The performances of the prior art unit and of the unit of the present invention are summarized in Table 1 below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 In accordance with 
                   
               
               
                   
                 Prior art 
                 the invention 
                 Units 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 H 2 /HC (sent to 
                 1.5 
                 0 
                 mol/mol 
               
               
                 reactor R1) 
               
               
                 H 2 /HC (sent to 
                 0 
                 1.5 
                 mol/mol 
               
               
                 reactor R3) 
               
               
                 C5+ 
                 90.1 
                 91.3 
                 wt % 
               
               
                 H 2   
                 3.6 
                 3.9 
                 wt % 
               
               
                 C1-C4 
                 6.3 
                 4.8 
                 wt % 
               
               
                 Consumption of 
                 3620 
                 2250 
                 kW 
               
               
                 recycle compressor 
               
               
                 (RCY) 
               
               
                 Compression ratio 
                 2.1 
                 1.6 
               
               
                 of recycle compressor 
               
               
                 Pressure 
                 3.5 
                 1.9 
                 bar 
               
               
                 differential of 
               
               
                 recycle compressor 
               
               
                 H 2 O supply 
                 4 
                 1.4 
                 ppm by weight 
               
               
                 Chlorine loss 
                 Base 
                 −30% 
                 relative 
               
               
                   
               
             
          
         
       
     
         [0080]    Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
         [0081]    In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
         [0082]    The entire disclosures of all applications, patents and publications, cited herein and of corresponding French application No. 10/02425, filed Jun. 9, 2010, are incorporated by reference herein. 
         [0083]    The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 
         [0084]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.