to saturate the diolefins. In some cases, the effluent of the DIOS may be split into two
in a splitter with the splitter overhead (LCN) either being sulfur-free (Prime-G+
™
) or
being subjected to a mercaptan extraction process (e.g., Merox or Exomer) and the
splitter botts then routed to the selective desulfurization reactor.
Reactions occurring in the selective desulfurization reactor include:
Desulfurization
R-S-R
0
þ 2H 2 ! RH þ R
0 H þ H 2 S
Olefin saturation
R ¼ R
0
þ 2H 2 ! RH-R
0 H
Recombination
R ¼ R
0
þ H 2 S $ R-R
0 -SH
Olefin drainage
R ¼ R
0
þ H 2 S $ R-R
0 -SH
R-R
0 -SH þ H 2 ! R-R
0
þ H 2 S
While all these reactions are exothermic, the catalysts are so selective that
desulfurization takes place to a much greater degree than olefin saturation, and
hence the temperature rise can be kept to manageable levels.
Process Configurations
The simplest process configuration consists of a DIOS followed by a selective
desulfurization reactor and a product stripper to remove H 2 S (Fig. 12).
Such a simple process configuration would be satisfactory when feed sulfur
levels are low, typically less than ~300 wppm. In such cases, it is possible to
achieve very low product sulfur levels, <10 wppm, with minimal saturation of
olefins and good octane retention.
A more complex process configuration would be required when the feed sulfur
content is higher than ~300 wppm. In this case, the feed is first routed to a DIOS
reactor to saturate the diolefins with the effluent of the DIOS entering a splitter with
the LCN sent overhead and the bottoms routed to a selective desulfurization reactor.
The splitter overhead may be subjected to a process such as UOP’s Merox Process
™
to extract the light mercaptans (Fig. 13).
A modification of the above process is Axens Prime-G+
™ , wherein the thioetherification function inherent in the diolefin saturation/selective hydrogenation catalyst, or SHU
™
, is also applied. The light mercaptans are converted to higher-boiling
sulfides by reaction with olefins. The sulfides thus formed boil at a much higher
400
P. Kokayeff et al.
in a splitter with the splitter overhead (LCN) either being sulfur-free (Prime-G+
™
) or
being subjected to a mercaptan extraction process (e.g., Merox or Exomer) and the
splitter botts then routed to the selective desulfurization reactor.
Reactions occurring in the selective desulfurization reactor include:
Desulfurization
R-S-R
0
þ 2H 2 ! RH þ R
0 H þ H 2 S
Olefin saturation
R ¼ R
0
þ 2H 2 ! RH-R
0 H
Recombination
R ¼ R
0
þ H 2 S $ R-R
0 -SH
Olefin drainage
R ¼ R
0
þ H 2 S $ R-R
0 -SH
R-R
0 -SH þ H 2 ! R-R
0
þ H 2 S
While all these reactions are exothermic, the catalysts are so selective that
desulfurization takes place to a much greater degree than olefin saturation, and
hence the temperature rise can be kept to manageable levels.
Process Configurations
The simplest process configuration consists of a DIOS followed by a selective
desulfurization reactor and a product stripper to remove H 2 S (Fig. 12).
Such a simple process configuration would be satisfactory when feed sulfur
levels are low, typically less than ~300 wppm. In such cases, it is possible to
achieve very low product sulfur levels, <10 wppm, with minimal saturation of
olefins and good octane retention.
A more complex process configuration would be required when the feed sulfur
content is higher than ~300 wppm. In this case, the feed is first routed to a DIOS
reactor to saturate the diolefins with the effluent of the DIOS entering a splitter with
the LCN sent overhead and the bottoms routed to a selective desulfurization reactor.
The splitter overhead may be subjected to a process such as UOP’s Merox Process
™
to extract the light mercaptans (Fig. 13).
A modification of the above process is Axens Prime-G+
™ , wherein the thioetherification function inherent in the diolefin saturation/selective hydrogenation catalyst, or SHU
™
, is also applied. The light mercaptans are converted to higher-boiling
sulfides by reaction with olefins. The sulfides thus formed boil at a much higher
400
P. Kokayeff et al.