Process for Pre-Refining Crude Oil with Moderate Multi-Step Hydroconversion of Virgin Asphalt in the Presence of Diluent

Abstract

For pre-refining a crude oil P, which P is fractionated into several fractions, typically hydrotreating, hydrocracking or hydroconverting some thereof, then re-composing said fractions and in general producing at least two pre-refined oils Pa, Pc, Pa being a high quality non-asphaltenic oil and Pc being a residual oil. The process typically comprises at least one initial distillation step and one deasphalting step SDA with a solvent with a molecular weight of at least 50 to separate a deasphalted oil DAO from a virgin asphalt stream AS. AS is hydroconverted in at least 2 ebullated bed reactors in series, with a moderate conversion of less than 56%, mixed with a virgin diluent comprising light fractions. The DAO is typically hydrocracked with a limited conversion of less than 80%.

1 . A process for pre-refining at least one crude oil P, comprising:
 at least one first step F 1  comprising initial fractionation by distillation, (PRE-DIST), to produce a first asphaltenic residue R 1  and at least one first non-asphaltenic stream E 1 ;   at least one second step F 2  comprising fractionation of at least a portion or fraction derived from R 1  by deasphalting (SDA) with a hydrocarbon solvent with a mean molecular weight of more than 50, to produce at least: firstly, a second non-asphaltenic stream E 2  comprising at least 50% by weight of virgin deasphalted oil included in the residue R 1 , and secondly a virgin asphalt AS; and   passing a heavy asphaltenic stream ASF to a unit RHDC for ebullated bed hydroconversion of residues, the ASF comprising at least 50% by weight of virgin asphalt AS and at least one diluent DIL which is liquid at ambient temperature and comprise at least 30% by weight of compounds derived from P boiling below 340° C., in which said diluent represents 3% to 40% by weight with respect to the asphalt included in the ASF, and conducting said ebullated bed residue hydroconversion unit RHDC in at least two hydroconversion steps in series in at least two ebullated bed reactors in series, the flow rate of the heavy asphaltenic stream being sufficiently high, and the dimensions of said two reactors being selected in relation with said flow rate so that conversion of the feed ASF into products boiling below 524° C. is over 30% by weight but less than 56% by weight, so as to obtain an asphaltenic hydroconversion effluent HAS with a sulphur content in the fraction which is non distillable at 524° C. and which is reduced with respect to the ASF, so as to produce at least one pre-refined asphaltenic oil Pc comprising at least the major portion of residual asphaltenes included in the HAS.   
   
   
       2 . A process according to  claim 1 , in which at least one pre-refined non-asphaltenic oil Pa is produced from non-asphaltenic cuts derived from P, optionally after catalytic hydrogenating treatment(s). 
   
   
       3 . A process according to  claim 2 , in which hydrotreatment and/or hydrocracking and/or hydroconversion of the E 2  is carried out at a pressure of at least 8 MPa, with a conversion into products boiling below 524° C. of at most 80% by weight, to obtain an effluent HE 2  comprising a substantial fraction of hydrotreated deasphalted oil HDAO with a sulphur content reduced by at least 50% with respect to the amount of sulphur in the HAS fraction boiling above 524° C., mixing with at least the major portion of the HAS a stream comprising a first fraction F 1  of said hydrotreated deasphalted oil HDAO to produce said pre-refined asphaltenic oil Pc and a second fraction F 2  of said hydrotreated deasphalted oil HDAO is mixed, optionally after supplemental hydrotreatment, with other non-asphaltenic streams derived from P, optionally hydrotreated and/or hydrocracked and/or hydroconverted to obtain said non-asphaltenic pre-refined oil Pa. 
   
   
       4 . A process according to  claim 1 , in which the ASF is hydroconverted in the residue hydroconversion unit RHDC operating within at least 3 hydroconversion steps in series in at least 3 ebullated bed reactors in series. 
   
   
       5 . A process according to  claim 1 , in which the DIL comprises 3% to 30% by weight with respect to the asphalt included in the ASF of fractions boiling below 340° C. which are virgin or simply hydrotreated derived from P. 
   
   
       6 . A process according to  claim 1 , in which the DIL comprises a virgin fraction derived from P with a composition substantially identical to oil P. 
   
   
       7 . A process according to  claim 6 , in which the DIL comprises, in an amount of 4% to 40% by weight with respect to asphalt included in the ASF, a stream essentially constituted by desalted oil P. 
   
   
       8 . A process according to  claim 3 , in which the F 1  represents between 15% and 85% by weight of (F 1 +F 2 ). 
   
   
       9 . A process according to  claim 1 , in which Pa and Pc are two oils, each being a final product from pre-refining and passing said final product as an initial distillation feed to at least one oil refinery. 
   
   
       10 . A process according to  claim 9 , in which at least the major portion of Pa and/or Pc is transported via pipelines and oil tankers for use as said initial distillation feed for at least one oil refinery. 
   
   
       11 . A process according to  claim 1 , in which Pa and Pc each comprises at least 6% by weight of naphtha N, at least 10% by weight of middle distillates MD and at least 10% by weight of vacuum distillate VGO. 
   
   
       12 . A process according to  claim 2 , wherein Pa is subjected to a catalytic hydrogenating step prior to being derived from non-asphaltenic cut from Pc.