Indonesia or North Africa. The same is true for nitrogen levels. The other impurities
are not always present. In general, the hydrotreating reactions proceed in the
following descending order of ease: (organometallic) metals removal, olefin saturation, sulfur removal, nitrogen removal, oxygen removal, and halide removal. The
contaminant removal in residue hydrotreating involves controlled breaking of the
hydrocarbon molecule at the point where the sulfur, nitrogen, or oxygen atom is
joined to carbon atoms. Some aromatic saturation also occurs. The chemistry of
residue hydrotreating is essentially that of contaminant removal. Some cracking
occurs in residue hydrotreating, but it is normally less than 30 vol% of the fresh feed
charge.
In general, the hydrodesulfurization reaction consumes 100–150 SCFB/wt%
change (17–25 Nm
3 /m
3 /wt% change), and the hydrodenitrogenation reaction consumes 200–350 SCFB/wt% change (34–59 Nm
3 /m
3 /wt% change). Typically, the
heat released in hydrotreating is about 0.1–0.2
F/SCFB H 2 consumed (0.35–0.70
C/Nm
3 /m
3 H 2 ).
In general, the “general principles” concerning hydrotreating reaction rates,
heats of reaction, and hydrogen consumption are:
• Hydrodesulfurization and olefin hydrogenation are the most rapid reactions.
• Olefin hydrogenation liberates the most heat per unit of hydrogen consumed.
• Hydrodenitrogenation and hydrodearomatization are the most difficult reactions.
• Hydrogen consumption and heat of reaction are related.
Sulfur Removal
From the end of the last century until now, ultra-low-sulfur fuel specifications
continue to tighten. By 2020, it is anticipated that most of the industrialized
world will have legislated no more than 10 wppm sulfur in both motor gasoline
and diesel products, consistent with the desire to improve fuel economy and reduce
vehicle emissions. Timelines for these changes are summarized in Fig. 4
(TransportPolicy.Net 2014).
Sulfur removal occurs via the conversion to H 2 S of the organic sulfur compounds present in the feedstock. This conversion is sometimes referred to as
desulfurization or hydrodesulfurization (HDS). Sulfur is found throughout the
boiling range of petroleum fractions in the form of many hundreds of different
organic sulfur compounds which, in the naphtha-to-atmospheric residue range,
can all be classified as belonging to one of the following six sulfur types:
mercaptans, sulfides, disulfides, thiophenes, benzothiophenes, and
dibenzothiophenes. Typical reactions for each kind of sulfur compound are
shown below.
Mercaptans
R-SH þ H 2 ! R-H þ H 2 S
Hydrotreating in Petroleum Processing
371
are not always present. In general, the hydrotreating reactions proceed in the
following descending order of ease: (organometallic) metals removal, olefin saturation, sulfur removal, nitrogen removal, oxygen removal, and halide removal. The
contaminant removal in residue hydrotreating involves controlled breaking of the
hydrocarbon molecule at the point where the sulfur, nitrogen, or oxygen atom is
joined to carbon atoms. Some aromatic saturation also occurs. The chemistry of
residue hydrotreating is essentially that of contaminant removal. Some cracking
occurs in residue hydrotreating, but it is normally less than 30 vol% of the fresh feed
charge.
In general, the hydrodesulfurization reaction consumes 100–150 SCFB/wt%
change (17–25 Nm
3 /m
3 /wt% change), and the hydrodenitrogenation reaction consumes 200–350 SCFB/wt% change (34–59 Nm
3 /m
3 /wt% change). Typically, the
heat released in hydrotreating is about 0.1–0.2
F/SCFB H 2 consumed (0.35–0.70
C/Nm
3 /m
3 H 2 ).
In general, the “general principles” concerning hydrotreating reaction rates,
heats of reaction, and hydrogen consumption are:
• Hydrodesulfurization and olefin hydrogenation are the most rapid reactions.
• Olefin hydrogenation liberates the most heat per unit of hydrogen consumed.
• Hydrodenitrogenation and hydrodearomatization are the most difficult reactions.
• Hydrogen consumption and heat of reaction are related.
Sulfur Removal
From the end of the last century until now, ultra-low-sulfur fuel specifications
continue to tighten. By 2020, it is anticipated that most of the industrialized
world will have legislated no more than 10 wppm sulfur in both motor gasoline
and diesel products, consistent with the desire to improve fuel economy and reduce
vehicle emissions. Timelines for these changes are summarized in Fig. 4
(TransportPolicy.Net 2014).
Sulfur removal occurs via the conversion to H 2 S of the organic sulfur compounds present in the feedstock. This conversion is sometimes referred to as
desulfurization or hydrodesulfurization (HDS). Sulfur is found throughout the
boiling range of petroleum fractions in the form of many hundreds of different
organic sulfur compounds which, in the naphtha-to-atmospheric residue range,
can all be classified as belonging to one of the following six sulfur types:
mercaptans, sulfides, disulfides, thiophenes, benzothiophenes, and
dibenzothiophenes. Typical reactions for each kind of sulfur compound are
shown below.
Mercaptans
R-SH þ H 2 ! R-H þ H 2 S
Hydrotreating in Petroleum Processing
371