Environmental Engineering Reference
In-Depth Information
Adsorptive Desulfurization and Denitrification.
Mitsui Mining (2008) has
produced high-quality activated coke that is a carbonaceous, porous adsorbent/catalyzer
produced by thermal treatment of coal, yielding carbonization and activation. This
product is able to adsorb the sulfur oxides (SO
x
) and decompose nitrogen oxides (NO
x
)
catalytically into nitrogen and water in the presence of injected ammonia (NH
3
).
Activated coke is also able to remove toxic trace materials and heavy metals. Many
studies reported that sulfur- or nitrogen-containing compounds can be selectively
removed from petroleum products and other liquid fuels by use of nano-structured
adsorbents (Subramani et al., 2004; Pati et al., 2006). For example, adsorption of
thiophene from a thiophene-pentane mixture has been investigated using zinc-based
nanocrystalline aluminum oxide under ambient conditions (Yang et al., 2007). The
adsorptive experiments show that a 20 wt % Zn/Al
2
O
3
adsorbent has the highest
capacity, 2.8 mg-sulfur/g-adsorbent. Nanocrystalline ZnO doped with Ce has a very high
desulfurization activity in the normal atmosphere with a space velocity of 9500 h
-1
and
at 25
o
C without oxygen and with a molar ratio of Ce:Zn being 4:100 (Li et al., 2006).
Montmorillonite (MMT) is a natural layer-layer material. Zhao et al. (2006)
reported that a SiO
2
pillared montmorillonite, modified with nanoparticles of rare earth
oxides and transition metal oxides, is an excellent selective adsorbent for gasoline
desulfurization; its desulfurization ratio increases by 52% more than Na-MMT. Metallic
nickel nanoparticles were incorporated on mesoporous silica to remove sulfur
compounds in diesel selectively, and the sulfur adsorption capacity was strongly
dependent on the nickel loading and the average nickel particle size (Ko et al., 2007).
Magnetic adsorbents can easily be reclaimed and separated by magnetic fields. Shan et
al. (2004) reported that the magnetic alumina sorbent based on magnetite nanoparticles
can effectively adsorb polycyclic aromatics and polycyclic aromatic sulfur compounds
from model gasoline.
Microbial Desulfurization and Denitrification.
Selected microorganisms can
utilize many compounds containing nitrogen (N), sulfur (S) and oxygen (O) that exist in
fuels as substrates via a complex set of multiple biochemical and chemical reactions
(Premuzic et al., 1999). When the bioconversion happens, nitrogen and sulfur can be
removed from these compounds. Biocatalytic desulfurization (BDS) of petroleum
distillate is based on naturally occurring aerobic bacteria that can remove organically
bound sulfur in heterocycles of petroleum without degrading the fuel value of the
hydrocarbon matrix (McFarland, 1999). Some mesophilic and thermophilic DBT-
desulfurizing microorganisms have been isolated, such as
Rhodococcus
sp. strain
IGTS8,
Rhodococcus erythropolis
D-1,
R. erythropolis
H-2,
R. erythropolis
KA2-5-1,
and
Paenibacillus
sp. strain A11-2,
Bacillus subtilis
WU-S2B and
Mycobacterium phlei
WU-F1. These bacteria desulfurize DBT through the sulfur-specific degradation
pathway with the selective cleavage of carbon-sulfur (C-S) bonds without reducing the
energy content. The biocatalyst has been genetically engineered to have a high level of
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