Multiple dense phase risers to maximize aromatics yields for naphtha catalytic cracking

Abstract

Systems and methods for producing aromatics and olefins via catalytic cracking are disclosed. A naphtha feed stream and lift gas stream are fed into one or more dense phase riser reactors, each of which is operated with a high solid volume fraction, a high superficial velocity, high back mixing. The effluent streams from all the dense phase riser reactors is further separated, in a secondary reactor, into a gaseous product stream and a catalyst stream. The catalyst stream is stripped to remove the hydrocarbons absorbed on the catalyst particles. The stripped catalyst is regenerated in a regenerator.

1 . A method of producing aromatics; the method comprising:
 contacting, in a dense phase riser reactor, naphtha with catalyst particles under reaction conditions sufficient to produce a first product comprising one or more olefins and/or one or more aromatics, wherein the dense phase riser reactor is operated such that superficial gas velocity therein is in a range of 4 to 20 m/s;   flowing a mixture of the first product, the catalyst particles, and unreacted naphtha to a cyclone system disposed in a secondary reactor, wherein the secondary reactor is stacked on top of a regenerator;   separating, in the cyclone system, the first product from the catalyst particles;   stripping, in a stripper disposed in the regenerator, hydrocarbon vapor from the catalyst particles to produce stripped catalyst particles; and   regenerating, in the regenerator, the stripped catalyst particles.   
     
     
         2 . The method of  claim 1 , wherein the dense phase riser reactor has an internal diameter in a range of 2.0 to 2.75 m. 
     
     
         3 . The method of  claim 1 , wherein the dense phase riser reactor comprises a fluidized bed with a solids volume fraction (SVF) in a range of 0.1 to 0.2. 
     
     
         4 . The method of  claim 1 , wherein the stripper and the regenerator are operated with a plurality of dense phase riser reactors. 
     
     
         5 . The method of  claim 1 , wherein the one or more dense phase riser reactors are operated using a lift gas selected from the group consisting of nitrogen, methane, any inert gas, and combinations thereof. 
     
     
         6 . The method of  claim 5 , wherein the lift gas contains less than 10 wt. % steam. 
     
     
         7 . The method of  claim 1 , wherein the catalyst comprises particles of average diameter in a range of 75 to 120 μm. 
     
     
         8 . The method of  claim 1 , wherein the catalyst has a particle density of 1000 to 1400 kg/m 3 . 
     
     
         9 . The method of  claim 1 , wherein the first product comprises unreacted naphtha, aromatics, light olefins, lift gas, by-products, or combinations thereof. 
     
     
         10 . The method of  claim 1 , wherein the reaction conditions comprise a reaction temperature in a range of 670 to 730° C. 
     
     
         11 . The method of  claim 1 , wherein the reaction conditions comprise a weight hourly space velocity of 0.3 to 3 hr −1  and an average residence time of 1 to 5 s. 
     
     
         12 . The method of  claim 1 , wherein the dense phase riser reactor comprises a fluidized bed having a catalyst to oil weight ratio of 10 to 50. 
     
     
         13 . The method of  claim 1 , wherein the dense phase riser reactor is operated at a volumetric feed to lift gas ratio of 1.25 to 2.5. 
     
     
         14 . A reaction unit for producing aromatics, the reaction unit comprising:
 one or more dense phase riser reactors, wherein each of the dense phase riser reactors comprises:   a housing;   a feed inlet disposed on a lower half of the housing, adapted to receive a feed material into the housing;   a lift gas inlet disposed on bottom of the housing, adapted to receive a lift gas into the housing;   a catalyst inlet disposed at the bottom of the housing, adapted to receive catalyst into the housing;   an outlet disposed on top of the housing, adapted to release an effluent of the dense phase riser from the housing;   a secondary reactor in fluid communication with the outlet of each dense phase riser reactor, wherein the secondary reactor comprises one or more cyclones adapted to separate the effluent of the dense phase riser(s) into a gaseous stream comprising gaseous products and a solid stream comprising a catalyst; and   a regenerator in fluid communication with the secondary reactor, adapted to receive the solid stream from the secondary reactor and regenerate the catalyst of the solid stream, wherein the secondary reactor is stacked on top of the regenerator and the regenerator is in fluid communication with the catalyst inlet of each dense phase riser reactor.   
     
     
         15 . The reaction unit of  claim 14 , wherein the catalyst regeneration unit further comprises a stripper adapted to strip hydrocarbons absorbed on catalyst particles of the solid stream using a stripping gas before the catalyst is regenerated. 
     
     
         16 . The reaction unit of  claim 15 , wherein the stripping gas comprises nitrogen, methane, flue gas, or combinations thereof. 
     
     
         17 . The reaction unit of  claim 14 , wherein the regenerator further comprises one or more cyclones adapted to separate flue gas from the catalyst. 
     
     
         18 . The reaction unit of  claim 15 , wherein the regenerator further comprises one or more cyclones adapted to separate flue gas from the catalyst. 
     
     
         19 . The reaction unit of  claim 16 , wherein the regenerator further comprises one or more cyclones adapted to separate flue gas from the catalyst. 
     
     
         20 . The method of  claim 3 , wherein the dense phase riser reactor is operated at a volumetric feed to lift gas ratio of 1.25 to 2.5.