Abstract: Fischer-Tropsch synthesis is one of the most
important catalytic reactions that convert the synthetic gas to light
and heavy hydrocarbons. One of the main issues is selecting the type
of reactor. The slurry bubble reactor is suitable choice for Fischer-
Tropsch synthesis because of its good qualification to transfer heat
and mass, high durability of catalyst, low cost maintenance and
repair. The more common catalysts for Fischer-Tropsch synthesis are
Iron-based and Cobalt-based catalysts, the advantage of these
catalysts on each other depends on which type of hydrocarbons we
desire to produce. In this study, Fischer-Tropsch synthesis is modeled
with Iron and Cobalt catalysts in a slurry bubble reactor considering
mass and momentum balance and the hydrodynamic relations effect
on the reactor behavior. Profiles of reactant conversion and reactant
concentration in gas and liquid phases were determined as the
functions of residence time in the reactor. The effects of temperature,
pressure, liquid velocity, reactor diameter, catalyst diameter, gasliquid
and liquid-solid mass transfer coefficients and kinetic
coefficients on the reactant conversion have been studied. With 5%
increase of liquid velocity (with Iron catalyst), H2 conversions
increase about 6% and CO conversion increase about 4%, With 8%
increase of liquid velocity (with Cobalt catalyst), H2 conversions
increase about 26% and CO conversion increase about 4%. With
20% increase of gas-liquid mass transfer coefficient (with Iron
catalyst), H2 conversions increase about 12% and CO conversion
increase about 10% and with Cobalt catalyst H2 conversions increase
about 10% and CO conversion increase about 6%. Results show that
the process is sensitive to gas-liquid mass transfer coefficient and
optimum condition operation occurs in maximum possible liquid
velocity. This velocity must be more than minimum fluidization
velocity and less than terminal velocity in such a way that avoid
catalysts particles from leaving the fluidized bed.
Abstract: Carbon nanotubes (CNTs) with their high mechanical,
electrical, thermal and chemical properties are regarded as promising
materials for many different potential applications. Having unique
properties they can be used in a wide range of fields such as
electronic devices, electrodes, drug delivery systems, hydrogen
storage, textile etc. Catalytic chemical vapor deposition (CCVD) is a
common method for CNT production especially for mass production.
Catalysts impregnated on a suitable substrate are important for
production with chemical vapor deposition (CVD) method. Iron
catalyst and MgO substrate is one of most common catalyst-substrate
combination used for CNT. In this study, CNTs were produced by
CCVD of acetylene (C2H2) on magnesium oxide (MgO) powder
substrate impregnated by iron nitrate (Fe(NO3)3•9H2O) solution. The
CNT synthesis conditions were as follows: at synthesis temperatures
of 500 and 800°C multiwall and single wall CNTs were produced
respectively. Iron (Fe) catalysts were prepared by with Fe:MgO ratio
of 1:100, 5:100 and 10:100. The duration of syntheses were 30 and
60 minutes for all temperatures and catalyst percentages. The
synthesized materials were characterized by thermal gravimetric
analysis (TGA), transmission electron microscopy (TEM) and Raman
spectroscopy.
Abstract: Hydrothermally synthesized high silica borosilicates
with the MFI structure was subjected to several characterization
techniques. The effect of boron on the structure and acidity of
HZSM-5 catalyst were studied by XRD, SEM, N2 adsorption, solid
state NMR, NH3-TPD. It was confirmed that boron had entered the
framework in the boron samples. The results also revealed that strong
acidity was weakened and weak acidity was strengthened by the
boron added zeolite framework compared with parent catalyst. The
catalytic performance was carried out in a fixed bed at 460°C for
methanol to propylene (MTP) reaction. The results of MTP reaction
showed a great increment of the propylene selectivity and excellent
stability for the B-HZSM-5. The catalyst exhibited about 81%
selectivity to C2
= - C4
= olefins with 40% selectivity of propylene as
major component at near 100% methanol conversion, and the stable
performance in the studied period was 100h.
Abstract: Intermetallic Ni3Al – based alloys belong to a group
of advanced materials characterized by good chemical and physical
properties (such as structural stability, corrosion resistance) which
offer advenced technological applications. The paper presents the
study of catalytic properties of Ni3Al foils (thickness approximately
50 &m) in the methanol and hexane decomposition. The egzamined
material posses microcrystalline structure without any additional
catalysts on the surface. The better catalytic activity of Ni3Al foils
with respect to quartz plates in both methanol and hexane
decomposition was confirmed. On thin Ni3Al foils the methanol
conversion reaches approximately 100% above 480 oC while the
hexane conversion reaches approximately 100% (98,5%) at 500 oC.
Deposit formed during the methanol decomposition is built up of
carbon nanofibers decorated with metal-like nanoparticles.
Abstract: A large number of chemical, bio-chemical and pollution-control processes use heterogeneous fixed-bed reactors. The use of finite hollow cylindrical catalyst pellets can enhance conversion levels in such reactors. The absence of the pellet core can significantly lower the diffusional resistance associated with the solid phase. This leads to a better utilization of the catalytic material, which is reflected in the higher values for the effectiveness factor, leading ultimately to an enhanced conversion level in the reactor. It is however important to develop a rigorous heterogeneous model for the reactor incorporating the two-dimensional feature of the solid phase owing to the presence of the finite hollow cylindrical catalyst pellet. Presently, heterogeneous models reported in the literature invariably employ one-dimension solid phase models meant for spherical catalyst pellets. The objective of the paper is to present a rigorous model of the fixed-bed reactors containing finite hollow cylindrical catalyst pellets. The reaction kinetics considered here is the widely used Michaelis–Menten kinetics for the liquid-phase bio-chemical reactions. The reaction parameters used here are for the enzymatic degradation of urea. Results indicate that increasing the height to diameter ratio helps to improve the conversion level. On the other hand, decreasing the thickness is apparently not as effective. This could however be explained in terms of the higher void fraction of the bed that causes a smaller amount of the solid phase to be packed in the fixed-bed bio-chemical reactor.
Abstract: Hydrogenated biodiesel is one of the most promising
renewable fuels. It has many advantages over conventional biodiesel,
including higher cetane number, higher heating value, lower
viscosity, and lower corrosiveness due to its absence of oxygen.
From previous work, Pd/TiO2 gave high conversion and selectivity in
hydrogenated biodiesel. In this work, the effect of biomass feedstocks
(i.e. beef fat, chicken fat, pork fat, and jatropha oil) on the production
of hydrogenated biodiesel over Pd/TiO2 has been studied. Biomass
feedstocks were analyzed by ICP-OES (inductively coupled plasma
optical emission spectrometry) to identify the content of impurities
(i.e. P, K, Ca, Na, and Mg). The deoxygenation catalyst, Pd/TiO2,
was prepared by incipient wetness impregnation (IWI) and tested in a
continuous flow packed-bed reactor at 500 psig, 325°C, H2/feed
molar ratio of 30, and LHSV of 4 h-1 for its catalytic activity and
selectivity in hydrodeoxygenation. All feedstocks gave high
selectivity in diesel specification range hydrocarbons and the main
hydrocarbons were n-pentadecane (n-C15) and n-heptadecane (n-
C17), resulting from the decarbonylation/decarboxylation reaction.
Intermediates such as oleic acid, stearic acid, palmitic acid, and esters
were also detected in minor amount. The conversion of triglycerides
in jatropha oil is higher than those of chicken fat, pork fat, and beef
fat, respectively. The higher concentration of metal impurities in
feedstock, the lower conversion of feedstock.
Abstract: Heterogeneous catalysis is vital for a number of
chemical, refinery and pollution control processes. The use of
catalyst pellets of hollow cylindrical shape provide several distinct
advantages over other common shapes, and can therefore help to
enhance conversion levels in reactors. A better utilization of the
catalytic material is probably most notable of these features due to
the absence of the pellet core, which helps to significantly lower the
effect of the internal transport resistance. This is reflected in the
enhancement of the effectiveness factor. For the case of the first order
irreversible kinetics, a substantial increase in the effectiveness factor
can be obtained by varying shape parameters. Important shape
parameters of a finite hollow cylinder are the ratio of the inside to the
outside radii (κ) and the height to the diameter ratio (γ). A high value
of κ the generally helps to enhance the effectiveness factor. On the
other hand, lower values of the effectiveness factors are obtained
when the dimension of the height and the diameter are comparable.
Thus, the departure of parameter γ from the unity favors higher
effectiveness factor. Since a higher effectiveness factor is a measure
of a greater utilization of the catalytic material, higher conversion
levels can be achieved using the hollow cylindrical pellets possessing
optimized shape parameters.
Abstract: The desulfurization of coal using biological methods is an emerging technology. The biodesulfurization process uses the catalytic activity of chemolithotrophic acidpohiles in removing sulfur and pyrite from the coal. The present study was undertaken to examine the potential of Acidithiobacillus ferrooxidans in removing the pyritic sulfur and iron from high iron and sulfur containing US coal. The experiment was undertaken in 10 L batch stirred tank reactor having 10% pulp density of coal. The reactor was operated under mesophilic conditions and aerobic conditions were maintained by sparging the air into the reactor. After 35 days of experiment, about 64% of pyrite and 21% of pyritic sulfur was removed from the coal. The findings of the present study indicate that the biodesulfurization process does have potential in treating the high pyrite and sulfur containing coal. A good mass balance was also obtained with net loss of about 5% showing its feasibility for large scale application.
Abstract: The nature of adsorbed species on catalytic surface
over an industrial precipitated iron-based high temperature catalyst
during FTS was investigated by in-situ DRIFTS and chemical
trapping. The formulation of the mechanism of oxygenates formation
and key intermediates were also discussed. Numerous oxygenated
precursors and crucial intermediates were found by in-situ DRIFTS,
such as surface acetate, acetyl and methoxide. The results showed that
adsorbed molecules on surface such as methanol or acetaldehyde
could react with basic sites such as lattice oxygen or free surface
hydroxyls. Adsorbed molecules also had reactivity of oxidizing.
Moreover, acetyl as a key intermediate for oxygenates was observed
by investigation of CH3OH + CO and CH3I + CO + H2. Based on the
nature of surface properties, the mechanism of oxygenates formation
on precipitated iron-based high temperature catalyst was discussed.
Abstract: Renewable energy sources have gained ultimate urgency due to the need of the preservation of the environment for a sustainable development. Pyrolysis is an ultimate promising process in the recycling and acquisition of precious chemicals from wastes. Here, the co-pyrolysis of hazelnut shell with ultra-high molecular weight polyethylene was carried out catalytically and noncatalytically at 500 and 650 ºC. Potassium dichromate was added in certain amounts to act as a catalyst. The liquid, solid and gas products quantities were determined by gravimetry. As a main result, remarkable increases in gasification were observed by using this catalyst for pure components and their blends especially at 650 ºC. The increase in gas product quantity was compensated mainly with the decreases in the solid products and additionally in some cases liquid products quantities. These observations may stem from mainly the activation of carbon-carbon bonds rather than carbon-hydrogen bonds via potassium dichromate. Also, the catalytic effect of potassium dichromate on HS: PEO and HS: UHMWPE co-pyrolysis was compared.
Abstract: The steam cracking reactions are always accompanied with the formation of coke which deposits on the walls of the tubular reactors. The investigation has attempted to control catalytic coking by the applying aluminum, zinc and ceramic coating like aluminum-magnesium by thermal spray and pack cementation method. Rate of coke formation during steam cracking of naphtha has been investigated both for uncoated stainless steel (with different alloys) and metal coating constructed with thermal Spray and pack cementation method with metal powders of Aluminum, Aluminum-Magnesium, zinc, silicon, nickel and chromium. The results of the study show that passivating the surface of SS321 with a coating of Aluminum and Aluminum-Magnesium can significantly reduce the rate of coke deposition during naphtha pyrolysis. SEM and EDAX techniques (Philips XL Series) were used to examine the coke deposits formed by the metal-hydrocarbon reactions. Our objective was to separate the different stages by identifying the characteristic morphologies.
Abstract: EcoDam is an adenine-N6 DNA methyltransferase
that methylates the GATC sites in the Escherichia coli genome.
DNA-adenine methylation is not present in higher eukaryotes
including humans. These observations raise the possibility that dam
inhibitors may be used as anti-microbial agents. Polyphosphate
(Poly(P)) is an important metabolite and signaling molecule in
prokaryotes and eukaryotes. Here, by using gel retardation
experiments to investigate the competition of DNA binding by
EcoDam in the presence of polyphosphate, we found that Poly (P)
strongly interferes with DNA binding by EcoDam, while same
concentration of monophosphate does not. In addition, we
demonstrated that Poly (P) binding inhibits the activity of EcoDam
and our results suggest that Poly (P) led to strong inhibition of the
EcoDam catalytic activity, while monophosphate had only moderate
effect.
Abstract: This work aims to test the application of computational fluid dynamics (CFD) modeling to fixed bed catalytic cracking reactors. Studies of CFD with a fixed bed design commonly use a regular packing with N=2 to define bed geometry. CFD allows us to obtain a more accurate view of the fluid flow and heat transfer mechanisms present in fixed bed equipment. Naphtha was used as feedstock and the reactor length was 80cm. It is divided in three sections that catalyst bed packed in the middle section of the reactor. The reaction scheme was involved one primary reaction and 24 secondary reactions. Because of high CPU times in these simulations, parallel processing have been used. In this study the coke formation process in fixed bed and empty tube reactor was simulated and coke in these reactors are compared. In addition, the effect of steam ratio and feed flow rate on coke formation was investigated.
Abstract: Copolymerization of ethylene with 1-hexene was
carried out using two ansa-fluorenyl titanium derivative complexes.
The substituent effect on the catalytic activity, monomer reactivity
ratio and polymer property was investigated. It was found that the
presence of t-Bu groups on fluorenyl ring exhibited remarkable
catalytic activity and produced polymer with high molecular weight.
However, these catalysts produce polymer with narrow molecular
weight distribution, indicating the characteristic of single-site
metallocene catalyst. Based on 13C NMR, we can observe that
monomer reactivity ratio was affected by catalyst structure. The rH
values of complex 2 were lower than that of complex 1 which might
be result from the higher steric hindrance leading to a reduction of 1-
hexene insertion step.
Abstract: A rigorous two-dimensional model is developed for simulating the operation of a less-investigated type steam reformer having a considerably lower operating Reynolds number, higher tube diameter, and non-availability of extra steam in the feed compared with conventional steam reformers. Simulation results show that reasonable predictions can only be achieved when certain correlations for wall to fluid heat transfer equations are applied. Due to severe operating conditions, in all cases, strong radial temperature gradients inside the reformer tubes have been found. Furthermore, the results show how a certain catalyst loading profile will affect the operation of the reformer.
Abstract: In the present study, a heterogeneous and
homogeneous gas flow dispersion model for simulation and
optimisation of a large-scale catalytic slurry reactor for the direct
synthesis of dimethyl ether (DME) from syngas and CO2, using a
churn-turbulent regime was developed. In the heterogeneous gas flow
model the gas phase was distributed into two bubble phases: small
and large, however in the homogeneous one, the gas phase was
distributed into only one large bubble phase. The results indicated
that the heterogeneous gas flow model was in more agreement with
experimental pilot plant data than the homogeneous one.
Abstract: β-Glucosidase is an important enzyme for production
of ethanol from lignocellulose. With hydrolytic activity on
cellooligosaccharides, especially cellobiose, β-glucosidase removes
product inhibitory effect on cellulases and forms fermentable sugars.
In this study, β-glucosidase encoding gene (BGL1) from traditional
starter yeast Saccharomycosis fibuligera BMQ908 was cloned and
expressed in Pichia pastoris. BGL1 of S. fibuligera BMQ 908 shared
98% nucleotide homology with the closest GenBank sequence
(M22475) but identity in amino-acid sequences of catalytic domains.
Recombinant plasmid pPICZαA/BGL1 containing the sequence
encoding BGL1 mature protein and α-factor secretion signal was
constructed and transformed into methylotrophic yeast P. pastoris by
electroporation. The recombinant strain produced single extracellular
protein with molecular weight of 120 kDa and cellobiase activity of
60 IU/ml. The optimum pH of the recombinant β-glucosidase was 5.0
and the optimum temperature was 50°C.
Abstract: Highly ordered arrays of TiO2 nanotubes (TiNTs) were grown vertically on Ti foil by electrochemical anodization. We controlled the lengths of these TiNTs from 2.4 to 26.8 ¶üÇóμm while varying the water contents (1, 3, and 6 wt%) of the electrolyte in ethylene glycol in the presence of 0.5 wt% NH4F with anodization for various applied voltages (20–80 V), periods (10–240 min) and temperatures (10–30 oC). For vertically aligned TiNT arrays, not only the increase in their tube lengths, but also their geometric (wall thickness and surface roughness) and crystalline structure lead to a significant influence on photocatalytic activity. The length optimization for methylene blue (MB) photodegradation was 18 μm. Further extending the TiNT length yielded lower photocatalytic activity presumably related to the limited MB diffusion and light-penetration depth into the TiNT arrays. The results indicated that a maximum MB photodegradation rate was obtained for the discrete anatase TiO2 nanotubes with thick and rough walls.
Abstract: Recently, a growing interest has emerged on the
development of new and efficient energy sources, due to the inevitable extinction of the nonrenewable energy reserves. One of
these alternative sources which has a great potential and sustainability to meet up the energy demand is biomass energy. This
significant energy source can be utilized with various energy
conversion technologies, one of which is biomass gasification in
supercritical water.
Water, being the most important solvent in nature, has very important characteristics as a reaction solvent under supercritical
circumstances. At temperatures above its critical point (374.8oC and
22.1 MPa), water becomes more acidic and its diffusivity increases.
Working with water at high temperatures increases the thermal
reaction rate, which in consequence leads to a better dissolving of the
organic matters and a fast reaction with oxygen. Hence, supercritical water offers a control mechanism depending on solubility, excellent
transport properties based on its high diffusion ability and new reaction possibilities for hydrolysis or oxidation.
In this study the gasification of a real biomass, namely olive mill
wastewater (OMW), in supercritical water is investigated with the
use of Pt/Al2O3 and Ni/Al2O3 catalysts. OMW is a by-product
obtained during olive oil production, which has a complex nature
characterized by a high content of organic compounds and
polyphenols. These properties impose OMW a significant pollution
potential, but at the same time, the high content of organics makes
OMW a desirable biomass candidate for energy production.
All of the catalytic gasification experiments were made with five
different reaction temperatures (400, 450, 500, 550 and 600°C),
under a constant pressure of 25 MPa. For the experiments conducted
with Ni/Al2O3 catalyst, the effect of five reaction times (30, 60, 90,
120 and 150 s) was investigated. However, procuring that similar
gasification efficiencies could be obtained at shorter times, the experiments were made by using different reaction times (10, 15, 20,
25 and 30 s) for the case of Pt/Al2O3 catalyst. Through these experiments, the effects of temperature, time and catalyst type on the
gasification yields and treatment efficiencies were investigated.
Abstract: The kinetics of palm oil catalytic cracking over
aluminum containing mesoporous silica Al-MCM-41 (5% Al) was
investigated in a batch autoclave reactor at the temperatures range of
573 – 673 K. The catalyst was prepared by using sol-gel technique
and has been characterized by nitrogen adsorption and x-ray
diffraction methods. Surface area of 1276 m2/g with average pore
diameter of 2.54 nm and pore volume of 0.811 cm3/g was obtained.
The experimental catalytic cracking runs were conducted using 50 g
of oil and 1 g of catalyst. The reaction pressure was recorded at
different time intervals and the data were analyzed using Levenberg-
Marquardt (LM) algorithm using polymath software. The results
show that the reaction order was found to be -1.5 and activation
energy of 3200 J/gmol.