Method for treating plastic pyrolysis oil including an h2s recycling step

Abstract

The present invention relates to a process for the treatment of a plastics pyrolysis oil, comprising:a hydrotreating of the feedstock in the presence of hydrogen and of a catalyst,a separation/scrubbing of the hydrotreated effluent in the presence of an aqueous solution in order to obtain at least a first aqueous effluent and a hydrotreated hydrocarbon effluent,a separation of the H2S contained in the first aqueous effluent, in order to obtain a gas phase containing the H2S and a second aqueous effluent, it being possible for said gas phase containing the H2S to be, at least partly, recycled upstream of stage b),a separation of the NH3 contained in the second aqueous effluent in order to obtain a gas phase containing NH3 and a third aqueous effluent.The present invention makes it possible, by the recycling of the H2S resulting from the process, to decrease the consumption of sulfiding agent for keeping the catalysts in the sulfide form in feedstocks containing only a little sulfur.

1 . A process for the treatment of a feedstock comprising a plastics pyrolysis oil, comprising:
 a) optionally a hydrogenation stage carried out in a hydrogenation reaction section, employing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrogenation catalyst, said hydrogenation reaction section being fed at least with said feedstock and a gas stream comprising hydrogen, said hydrogenation reaction section being employed at an average temperature between 140 and 400° C., a hydrogen partial pressure between 1.0 and 10.0 MPa abs. and an hourly space velocity between 0.1 and 10.0 h −1 , in order to obtain a hydrogenated effluent,   b) a hydrotreating stage carried out in a hydrotreating reaction section comprising at least one hydrotreating catalyst, said hydrotreating reaction section being fed at least with the feedstock or said hydrogenated effluent resulting from stage a) and a gas stream comprising hydrogen, said hydrotreating reaction section being employed at an average temperature between 250 and 430° C., a hydrogen partial pressure between 1.0 and 10.0 MPa abs. and an hourly space velocity between 0.1 and 10.0 h −1 , in order to obtain a hydrotreated effluent,   c) a separation stage, fed with the hydrotreated effluent resulting from stage b) and optionally with the hydrocracked effluent resulting from stage g) and an aqueous solution, in order to obtain at least a gaseous effluent, a first aqueous effluent and a hydrocarbon effluent,   d) a stage of separation of the H 2 S contained in the first aqueous effluent, in order to obtain a gas phase containing the H 2 S and a second aqueous effluent, said gas phase containing the H 2 S being optionally, at least partly, recycled upstream of stage a) and/or stage b) and/or stage g),   e) a stage of separation of the NH 3  contained in the second aqueous effluent, in order to obtain a gas phase containing NH 3  and a third aqueous effluent, said gas phase containing NH 3  being optionally, at least in part, recycled upstream of stage a) and/or stage b) and/or stage g),   f) optionally a stage of fractionation of all or part of the hydrocarbon effluent resulting from stage c), in order to obtain at least a gaseous effluent and at least a first hydrocarbon cut comprising compounds having a boiling point of less than or equal to 175° C. and a second hydrocarbon cut comprising compounds having a boiling point of greater than 175° C., and   g) optionally, a hydrocracking stage carried out in a hydrocracking reaction section, employing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrocracking catalyst, said hydrocracking reaction section being fed with at least a part of said hydrocarbon effluent resulting from stage c) and/or with at least a part of the second hydrocarbon cut comprising compounds having a boiling point of greater than 175° C. resulting from stage f) and a gas stream comprising hydrogen, said hydrocracking reaction section being employed at an average temperature between 250 and 450° C., a hydrogen partial pressure between 1.5 and 20.0 MPa abs. and an hourly space velocity between 0.1 and 10.0 h −1 , in order to obtain a first hydrocracked effluent.   
     
     
         2 . The process according to  claim 1 , in which said gas phase containing the H 2 S resulting from stage d) is at least partly recycled upstream of stage a) and/or stage b) and/or stage g). 
     
     
         3 . The process according to  claim 1 , comprising the hydrogenation stage a). 
     
     
         4 . The process according to  claim 1 , comprising the fractionation stage f). 
     
     
         5 . The process according to  claim 1 , comprising the hydrocracking stage g). 
     
     
         6 . The process according to  claim 1 , in which stage d) of separation of the H 2 S contained in the first aqueous effluent is carried out by stripping said effluent with a stream containing steam at a pressure of between 0.5 and 1 MPa and a temperature of between 80 and 150° C. 
     
     
         7 . The process according to  claim 1 , in which stage e) of separation of the NH 3  contained in the second aqueous effluent is carried out by stripping said effluent with a stream containing steam at a pressure of between 0.1 and 0.5 MPa and a temperature of between 80 and 150° C. 
     
     
         8 . The process according to  claim 1 , in which the separation stage c) comprises the following stages:
 c1) a separation stage, fed with the hydrotreated effluent resulting from stage b), said stage being carried out at a temperature of between 200 and 450° C. and at a pressure substantially identical to the pressure of stage b), in order to obtain at least a gaseous effluent and a liquid effluent, a part of which is optionally recycled upstream of stage a) and/or of stage b),   c2) a separation stage, fed with the gaseous effluent resulting from stage c1) and another part of the liquid effluent resulting from stage c1) and an aqueous solution, said stage being carried out at a temperature of between 20 and less than 200° C. and at a pressure substantially identical to or less than the pressure of stage b), in order to obtain at least a gaseous effluent, a first aqueous effluent and a hydrocarbon effluent.   
     
     
         9 . The process according to  claim 1 , comprising at least one stage a0) of pretreatment of the feedstock comprising a plastics pyrolysis oil, optionally as a mixture with the hydrocarbon effluent resulting from stage c), said pretreatment stage being carried out upstream of stage a) and/or upstream of stage b), and comprises a filtration stage and/or a centrifugation stage and/or an electrostatic separation stage and/or a stage of scrubbing by means of an aqueous solution and/or an adsorption stage and/or a selective hydrogenation stage. 
     
     
         10 . The process according to  claim 1 , in which the hydrocarbon effluent resulting from the separation stage c), or at least one of the two liquid hydrocarbon cuts resulting from stage f), is sent, completely or partly, to a steam cracking stage h) carried out in at least one pyrolysis furnace at a temperature of between 700 and 900° C. and at a pressure of between 0.05 and 0.3 MPa relative. 
     
     
         11 . The process according to  claim 1 , in which said gas phase containing the NH 3  resulting from stage e) is at least partly recycled upstream of stage a) and/or stage b) and/or stage g). 
     
     
         12 . The process according to  claim 1 , in which a stream containing a nitrogen compound and/or a sulfur compound is injected upstream of stage a) and/or upstream of stage b). 
     
     
         13 . The process according to  claim 1 , in which said hydrogenation catalyst comprises a support chosen from alumina, silica, silicas-aluminas, magnesia, clays and their mixtures and a hydro-dehydrogenating function comprising either at least one element from group VIII and at least one element from group VIB, or at least one element from group VIII. 
     
     
         14 . The process according to  claim 1 , in which said hydrotreating catalyst comprises a support chosen from the group consisting of alumina, silica, silicas-aluminas, magnesia, clays and their mixtures and a hydro-dehydrogenating function comprising at least one element from group VIII and/or at least one element from group VIB. 
     
     
         15 . The process according to  claim 1 , which additionally comprises a second hydrocracking stage g′) carried out in a hydrocracking reaction section, employing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrocracking catalyst, said hydrocracking reaction section being fed with at least a part of the first hydrocracked effluent resulting from the first hydrocracking stage g) and a gas stream comprising hydrogen, said hydrocracking reaction section being employed at a temperature between 250 and 450° C., a hydrogen partial pressure between 1.5 and 20.0 MPa abs. and an hourly space velocity between 0.1 and 10.0 h −1 , in order to obtain a second hydrocracked effluent. 
     
     
         16 . The process according to  claim 1 , in which said hydrocracking catalyst comprises a support chosen from halogenated aluminas, combinations of boron and aluminum oxides, amorphous silicas-aluminas and zeolites and a hydro-dehydrogenating function comprising at least one metal from group VIB chosen from chromium, molybdenum and tungsten, alone or as a mixture, and/or at least one metal from group VIII chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum. 
     
     
         17 . A product obtained by the process according to  claim 1 . 
     
     
         18 . The product according to  claim 17 , which comprises, with respect to the total weight of the product:
 a total content of metal elements of less than or equal to 10.0 ppm by weight,   including a content of iron element of less than or equal to 200 ppb by weight, and/or   a content of silicon element of less than or equal to 5.0 ppm by weight, and/or   a sulfur content of less than or equal to 100 ppm by weight, and/or   a nitrogen content of less than or equal to 100 ppm by weight, and/or   a content of chlorine element of less than or equal to 10 ppm by weight, and/or   a mercury content of less than or equal to 5 ppb by weight.