Fouling reduction in supercritical extraction units

Abstract

A residual petroleum fraction feed is subjected to a deasphalting process by solvent extraction using a light paraffinic solvent with recovery of the solvent under supercritical process conditions. Fouling is reduced by the injection of an aromatic stream into the DAO-solvent stream from the extractor in order to provide a degree of solvency for residual asphaltenes in the DAO-solvent stream which otherwise would tend to precipitate in the heat exchanger used to create the supercritical conditions for the solvent. The aromatic solvent stream which, by its aromatic character, has solvency properties for the asphaltene components remaining in the DAO-solvent stream, is selected to have a boiling point above the boiling point of the solvent so that it does not contaminate the process solvent when the solvent is recovered in the solvent recovery section of the unit.

1 . A residual oil deasphalting process which comprises:
 (i) contacting a petroleum fraction containing asphaltenes with a light paraffinic solvent for the non-asphaltene portion of the oil to produce a solution of deasphalted oil in the solvent and an asphaltenes fraction,   (ii) passing the deasphalted oil solution through pressurization and heating steps to bring the solvent to a supercritical condition to cause a phase separation between a solvent-depleted solution of the deasphalted oil in the solvent and a phase comprising substantially solvent,   (iii) separating the solvent-depleted solution of the deasphalted oil from the substantially solvent phase,   (iv) recovering the deasphalted oil from the solvent-depleted solution, and   (v) mixing an aromatic oil having a boiling point above the boiling point of the solvent and solvency properties for residual asphaltene components in the first solution into the first solution prior to the heating step.   
     
     
         2 . A process according to  claim 1  in which the light paraffinic solvent comprises a C 4  to C 7  paraffin. 
     
     
         3 . A process according to  claim 1  in which the light paraffinic solvent comprises butane. 
     
     
         4 . A process according to  claim 1  in which the petroleum resid fraction comprises a fraction having an initial boiling point above 450° C. (842° F.). 
     
     
         5 . A process according to  claim 1  in which the petroleum fraction comprises a resid fraction having an initial boiling point above 550° C. (1022° F.). 
     
     
         6 . A process according to  claim 1  in which the aromatic oil has an initial boiling point of at least 345° C. (650° F.). 
     
     
         7 . A process according to  claim 1  which includes the step of separating the first deasphalted oil solution from the asphaltenes fraction. 
     
     
         8 . A process according to  claim 1  in which the aromatic oil comprises a lube extract. 
     
     
         9 . A process according to  claim 8  in which the aromatic oil comprises a lube extract having a boiling point of at least 345° C. (about 650° F.) with an aromatics content of at least 70 wt. pct. 
     
     
         10 . A process according to  claim 9  in which the aromatic oil comprises a lube extract having a boiling range from 345 to 595° C. (about 650-1100° F.) with an aromatics content of at least 85 wt. pct. 
     
     
         11 . A process according to  claim 1  in which the proportion of the aromatic oil relative to deasphalted oil is from 0.05 to 0.40 volume ratio (aromatic oil to deasphalted oil not including solvent). 
     
     
         12 . A process according to  claim 1  in which the proportion of the aromatic oil relative to the deasphalted oil is from 5 to 30 vol %. 
     
     
         13 . A process according to  claim 1  in which the proportion of the aromatic oil relative to the deasphalted oil is from 20 to 30 vol %. 
     
     
         14 . A process according to  claim 1  in which the aromatic oil is injected into the deasphalted oil-solvent solution upstream of the pressurization step. 
     
     
         15 . A residual oil deasphalting process which comprises:
 (i) extracting asphaltenes from a petroleum resid fraction by contacting the fraction with a light paraffinic solvent to produce a solution comprising deasphalted oil and residual amounts of asphaltenes in the solvent and an asphaltenes fraction,   (ii) mixing an aromatic oil having a boiling point above the boiling point of the solvent and solvency properties for residual asphaltene components in the solution into the solution,   (iii) passing the solution through pressurization and heating steps to bring the solvent to a supercritical condition to cause a phase separation between a solvent-depleted solution of the deasphalted oil and a phase comprising substantially solvent,   (iv) separating the solvent-depleted solution of the deasphalted oil from the substantially solvent phase,   (v) recovering the deasphalted oil from the solvent-depleted solution,   (vi) recovering solvent from the substantial solvent phase and from the solvent-depleted solution,   (vii) recycling the recovered solvent to the extraction step.   
     
     
         16 . A process according to  claim 15  which includes the step of separating the solution of deasphalted oil in the solvent from the asphaltenes fraction. 
     
     
         17 . A process according to  claim 15  in which the light paraffinic solvent comprises a butane. 
     
     
         18 . A process according to  claim 15  in which the petroleum resid fraction comprises a fraction having an initial boiling point above 450° C. (842° F.). 
     
     
         19 . A process according to  claim 15  in which the petroleum resid fraction comprises a fraction having an initial boiling point above 550° C. (1022° F.). 
     
     
         20 . A process according to  claim 15  in which the aromatic oil comprises a lube extract. 
     
     
         21 . A process according to  claim 15  in which the aromatic oil comprises a lube extract having a boiling point of at least 345° C. (about 650° F.) with an aromatics content of at least 70 wt. pct. 
     
     
         22 . A process according to  claim 15  in which the aromatic oil comprises a lube extract having a boiling range from 345 to 595° C. (about 650-1100° F.) with an aromatics content of at least 85 wt. pct. 
     
     
         23 . A process according to  claim 15  in which the proportion of the aromatic oil relative to deasphalted oil is from 0.05 to 0.40 volume ratio (aromatic oil to deasphalted oil not including solvent). 
     
     
         24 . A process according to  claim 15  in which the proportion of the aromatic oil relative to the deasphalted oil is from 5 to 30 vol %. 
     
     
         25 . A process according to  claim 15  in which the proportion of the aromatic oil relative to the deasphalted oil is from 20 to 30 vol %.