Process for the production of a desulfurized gasoline from a gasoline fraction that contains conversion gasoline

Abstract

Production of gasolines with low sulfur contents from a starting gasoline containing sulfur-containing compounds comprising a stage a) for selective hydrogenation of non-aromatic polyunsaturated compounds present in the starting gasoline, a stage b) for increasing the molecular weight of the light sulfur-containing products that are initially present in the gasoline that enters this stage, a stage c) for alkylation of at least a portion of the sulfur-containing compounds present in the product that originates stage b), a stage d) for fractionation of the gasoline that originates from stage c0 into at least two fractions, one fraction virtually lacking in sulfur-containing compounds, whereby the other contains a larger proportion of sulfur-containing compounds (heavy gasoline), a stage e) for catalytic treatment of the heavy gasoline for transformation of sulfur-containing compounds under conditions for the at least partial decomposition of hydrogenation of these sulfur-containing compounds.

1 . Process for the production of gasoline with a low sulfur content from a starting gasoline that contains at least 150 ppm by weight of sulfur-containing compounds comprising at least the following stages: 
 a stage a) for selective hydrogenation of non-aromatic, polyunsaturated compounds that are present in the starting gasoline,    at least one stage b) that aims at increasing the molecular weight of the light sulfur-containing products, primarily those that are in the form of mercaptans that have 1 to 6 carbon atoms in their molecules and sulfides that are initially present in the gasoline that is introduced in stage a) and/or those that are contained in the product that originates from stage a),    at least one stage c) for alkylation of at least a portion of the sulfur-containing compounds, primarily those that are in the form of thiophenic compounds that are present in the product that originates from stage b) that aims at obtaining sulfur-containing compounds with a higher molecular weight,    at least one stage d) for fractionation of the gasoline that originates from stage c) into at least two fractions, a first fraction that is virtually lacking in sulfur and that contains the lightest olefins of the unconverted starting gasoline in stage c), (light gasoline), at least one other fraction, heavier than said first fraction, enriched with sulfur-containing compounds, and    at least one stage e) for treatment of at least one of the heavier fractions that originates from stage d) on a catalyst that makes it possible to decompose at least partially the sulfur-containing compounds.    
     
     
         2 . Process according to  claim 1 , in which stage e) for treatment of at least one of the heavier fractions that is separated in stage d) on a catalyst that makes it possible to decompose at least partially the sulfur-containing compounds is carried out under conditions where the hydrogenation of olefins on this catalyst is limited.  
     
     
         3 . Process according to  claim 1  or  2  comprising at least one stage f) for treatment of the product that is obtained in stage e), without elimination of the H 2 S that is formed during this stage e), on a catalyst and under conditions that make it possible to decompose at least partially the sulfur-containing compounds that are not transformed during stage e) with a limited hydrogenation of olefins.  
     
     
         4 . Process according to one of  claims 1  to  3 , in which the starting gasoline is a catalytic cracking gasoline whose final boiling points are from about 120° C. to about 230° C.  
     
     
         5 . Process according to  claim 3  or  4 , in which the conditions of stage f) are selected so as to decompose the unsaturated sulfur-containing compounds and the linear and/or cyclic saturated sulfur-containing compounds that are not transformed during stage e), with a limited hydrogenation of olefins.  
     
     
         6 . Process according to one of  claims 1  to  5 , in which stage a) for hydrogenation of unsaturated compounds and stage b) that aims at increasing the molecular weight of the light sulfur-containing products that are initially present in the gasoline that is introduced in stage a) are carried out simultaneously in a single reaction zone that contains one or more beds of a single catalyst.  
     
     
         7 . Process according to one of  claims 1  to  6 , in which the starting gasoline contains basic nitrogen-containing compounds that are at least in part eliminated before stage c) for alkylation of at least a portion of the sulfur-containing compounds that are present in the product that originates from stage b).  
     
     
         8 . Process according to  claim 7 , in which the basic nitrogen-containing compounds that are contained in the starting gasoline are at least partly eliminated before its introduction into stage a) for hydrogenation of the polyunsaturated compounds.  
     
     
         9 . Process according to  claim 6  or  7 , in which the elimination of the basic nitrogen-containing compounds is carried out by a treatment with an acid aqueous solution.  
     
     
         10 . Process according to one of  claims 3  to  9 , in which the desulfurized heavy gasoline that originates from stage f) is subjected to a stripping treatment by means of a cover gas.  
     
     
         11 . Process according to one of  claims 3  to  10 , in which stages e) and f) are carried out in at least two successive and separate reaction zones.  
     
     
         12 . Process according to one of  claims 3  to  11 , in which the light gasoline that originates from stage d) and at least a portion of the heavy gasoline that originates from stage f) are mixed to form the overall desulfurized gasoline that is desired.  
     
     
         13 . Process according to one of  claims 1  to  12 , in which the catalyst of stage e) comprises at least one element of group VIII and at least one element of group VIB.  
     
     
         14 . Process according to one of  claims 3  to  13 , in which the catalyst of stage f) comprises at least one element of group VIII.  
     
     
         15 . Process according to one of  claims 3  to  14 , in which the catalysts that are used in stages e) and f) are separate sulfurized catalysts.  
     
     
         16 . Process according to one of  claims 3  to  15 , in which stages e) and f) are carried out in two reactors that are placed in series, whereby the second reactor treats the effluent of the first reactor as a whole.  
     
     
         17 . Process according to one of  claims 1  to  16 , in which alkylation stage c) is carried out under conditions such that a portion of the olefins of the starting gasoline is converted into long branched olefins by addition reactions between olefins and such that a portion of the aromatic compounds is increased in weight by alkylation by the olefins.  
     
     
         18 . Process according to one of  claims 1  to  17 , in which the heavy fraction that originates from stage d) is sent into a fractionation zone that makes it possible to obtain a heavy fraction that is enriched with sulfur and a lighter fraction that is low in sulfur.  
     
     
         19 . Process according to one of  claims 1  to  17 , in which the gasoline that originates from hydrodesulfurization stage e) or f) is sent into a fractionation zone that makes it possible to obtain a heavy fraction that is enriched with sulfur and a lighter fraction that is low in sulfur.