585
Hydrotreating and Desulfurization
most active catalyst for this, the extra expense is warranted. On the other hand, many refiners wish
only to make acceptable diesel, a less demanding application. For this, the less expensive molybdenum sulfides are adequate.
21.6 BIODESULFURIZATION
Refiners are being continually challenged to produce products with ever-decreasing levels of sulfur.
At the same time, the supplies of light, low sulfur crude oil that favor distillate production are limited
and even decreasing. Generally, the sulfur content of petroleum continues to rise (Speight, 2011a,b)
with the accompanying decrease in API gravity and an increase in the proportion of residua in the
crude oil. These factors require the crude oil to be processed more severely to produce gasoline and
other transportation fuels. Thus, many refineries are now configured for maximum gasoline production that also includes increasingly processing highly aromatic distillate byproducts, such as light
cycle oil, for the additional feedstock to produce more distillate.
In microbial-enhanced oil recovery processes (Chapters 6 and 7), microbial technology is
exploited in oil reservoirs to improve recovery. In the process, injected nutrients, together with
indigenous or added microbes, promote in situ microbial growth and/or generation of products
which mobilize additional oil and move it to producing wells through reservoir repressurization,
interfacial tension/oil viscosity reduction, and selective plugging of the most permeable zones.
Alternatively, the oil-mobilizing microbial products may be produced by fermentation and injected
into the reservoir.
Biocatalyst desulfurization of petroleum distillates is one of a number of possible modes of
applying biologically-based processing to the needs of the petroleum industry (McFarland et al.,
1998; Setti et al., 1999; Abbad-Andaloussi et al., 2003; Mohebali and Ball, 2008). In addition,
mycobacterium goodie has been found to desulfurize benzothiophene (Li et al., 2005). The desulfurization product was identified as α-hydroxystyrene. This strain appeared to have the ability to
remove organic sulfur from a broad range of sulfur species in gasoline. When straight-run gasoline
containing various organic sulfur compounds was treated with immobilized cells of mycobacterium goodie for 24 h at 40°C (104°F), the total sulfur content significantly decreased, from 227
to 71 ppm at 40°C. Furthermore, when immobilized cells were incubated at 40°C (104°F) with
mycobacterium goodie, the sulfur content of the gasoline decreased from 275 to 54 ppm in two
consecutive reactions.
A dibenzothiophene-degrading bacterial strain, Nocardia sp., was able to convert dibenzothiophene to 2-hydroxybiphenyl as the end metabolite through a sulfur-specific pathway (Chang et al.,
1998). Other organic sulfur compounds, such as thiophene derivatives, thiazole derivatives, sulfides,
and disulfides were also desulfurized by Nocardia sp. When a sample in which dibenzothiophene
was dissolved in hexadecane and treated with growing cells, the dibenzothiophene was desulfurized
in approximately 80 hr.
The soil-isolated strain microcobe identified as Rhodococcus erythropolis can efficiently
desulfurize benzonaphthothiophene (Yu et al., 2006). The desulfurization product was α-hydroxyß-phenyl-naphthalene. Resting cells were able to desulfurize diesel oil (total organic sulfur,
259 ppm) after hydrodesulfurization and the sulfur content of diesel oil was reduced by 94.5% after
24 h at 30°C (86°F). Biodesulfurization of crude oils was also investigated and after 72 h at 30°C
(86°F), 62.3% of the total sulfur content in Fushun crude oil (initial total sulfur content, 3210 ppm)
and 47.2% of the sulfur in Sudanese crude oil (initial total sulfur, 1237 ppm) were removed (see also
Abbad-Andaloussi et al., 2003 and references cited therein).
Heavy crude oil recovery, facilitated by microorganisms, was suggested in the 1920s and received
growing interest in the 1980s as microbial enhanced oil recovery. However, such projects have been
slow to get under way although in situ biosurfactant and biopolymer applications continue to garner
interest (Van Hamme et al., 2003, and references cited therein). In fact, studies have been carried
out on biological methods of removing heavy metals such as nickel and vanadium from petroleum
Hydrotreating and Desulfurization
most active catalyst for this, the extra expense is warranted. On the other hand, many refiners wish
only to make acceptable diesel, a less demanding application. For this, the less expensive molybdenum sulfides are adequate.
21.6 BIODESULFURIZATION
Refiners are being continually challenged to produce products with ever-decreasing levels of sulfur.
At the same time, the supplies of light, low sulfur crude oil that favor distillate production are limited
and even decreasing. Generally, the sulfur content of petroleum continues to rise (Speight, 2011a,b)
with the accompanying decrease in API gravity and an increase in the proportion of residua in the
crude oil. These factors require the crude oil to be processed more severely to produce gasoline and
other transportation fuels. Thus, many refineries are now configured for maximum gasoline production that also includes increasingly processing highly aromatic distillate byproducts, such as light
cycle oil, for the additional feedstock to produce more distillate.
In microbial-enhanced oil recovery processes (Chapters 6 and 7), microbial technology is
exploited in oil reservoirs to improve recovery. In the process, injected nutrients, together with
indigenous or added microbes, promote in situ microbial growth and/or generation of products
which mobilize additional oil and move it to producing wells through reservoir repressurization,
interfacial tension/oil viscosity reduction, and selective plugging of the most permeable zones.
Alternatively, the oil-mobilizing microbial products may be produced by fermentation and injected
into the reservoir.
Biocatalyst desulfurization of petroleum distillates is one of a number of possible modes of
applying biologically-based processing to the needs of the petroleum industry (McFarland et al.,
1998; Setti et al., 1999; Abbad-Andaloussi et al., 2003; Mohebali and Ball, 2008). In addition,
mycobacterium goodie has been found to desulfurize benzothiophene (Li et al., 2005). The desulfurization product was identified as α-hydroxystyrene. This strain appeared to have the ability to
remove organic sulfur from a broad range of sulfur species in gasoline. When straight-run gasoline
containing various organic sulfur compounds was treated with immobilized cells of mycobacterium goodie for 24 h at 40°C (104°F), the total sulfur content significantly decreased, from 227
to 71 ppm at 40°C. Furthermore, when immobilized cells were incubated at 40°C (104°F) with
mycobacterium goodie, the sulfur content of the gasoline decreased from 275 to 54 ppm in two
consecutive reactions.
A dibenzothiophene-degrading bacterial strain, Nocardia sp., was able to convert dibenzothiophene to 2-hydroxybiphenyl as the end metabolite through a sulfur-specific pathway (Chang et al.,
1998). Other organic sulfur compounds, such as thiophene derivatives, thiazole derivatives, sulfides,
and disulfides were also desulfurized by Nocardia sp. When a sample in which dibenzothiophene
was dissolved in hexadecane and treated with growing cells, the dibenzothiophene was desulfurized
in approximately 80 hr.
The soil-isolated strain microcobe identified as Rhodococcus erythropolis can efficiently
desulfurize benzonaphthothiophene (Yu et al., 2006). The desulfurization product was α-hydroxyß-phenyl-naphthalene. Resting cells were able to desulfurize diesel oil (total organic sulfur,
259 ppm) after hydrodesulfurization and the sulfur content of diesel oil was reduced by 94.5% after
24 h at 30°C (86°F). Biodesulfurization of crude oils was also investigated and after 72 h at 30°C
(86°F), 62.3% of the total sulfur content in Fushun crude oil (initial total sulfur content, 3210 ppm)
and 47.2% of the sulfur in Sudanese crude oil (initial total sulfur, 1237 ppm) were removed (see also
Abbad-Andaloussi et al., 2003 and references cited therein).
Heavy crude oil recovery, facilitated by microorganisms, was suggested in the 1920s and received
growing interest in the 1980s as microbial enhanced oil recovery. However, such projects have been
slow to get under way although in situ biosurfactant and biopolymer applications continue to garner
interest (Van Hamme et al., 2003, and references cited therein). In fact, studies have been carried
out on biological methods of removing heavy metals such as nickel and vanadium from petroleum