Methanol to Prop y Lene
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Transcript of Methanol to Prop y Lene
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2
Project of Heterogeneous catalysts
In The Name of God
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Outlines
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What is Propene?
Production
MTP Process
Mechanism & Kinetic
Catalyst
Template of Catalyst Synthesis
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What is Propene?
Propene, also known as propylene or methylethylene, is an
unsaturated organic compound having the chemical formula
C3H6. it is a colorless, low-boiling, flammable, and highly
volatile gas [1].
Propene is the second most important starting product in the
petrochemical industry after ethylene. Essentially all of the
propylene produced for chemical purposes is consumed as a
chemical intermediate in other chemical manufacturing
processes.
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Production
The steam cracking of NGL, naphtha or other light
fractions of petroleum.
By-product of gasoline production from larger FCC
units.
Higher catalyst-to-oil ratios, Higher steam
injection rates, Higher temperatures, etc.
Other methods : Thermal cracking of ethane,
MTP,
The propylene production distribution in
2009 was
70
% from
steam cracking at 52 mln tons,
25
% from FCC conversion at
19 mln tons and 5% from other methods (about 4 mln tons)
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MTP
Furthermore, the consumption of a large
amount of energy in the thermal cracking of
naphtha, along with the large carbon dioxide
emissions, increases the production cost of the
lower olefins [2].
The rapid increase in the price of crude oil has lowered the
feasibility of these processes for the production of the lower
olefins, because they are based on petroleum sources.
MTP produces propylene selectively from methanol, it can be
produced from synthesis gas, which can be made from any
source of carbon-containing materials such coal, petroleum
residue, biomass and natural gas.
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MTP
MTP Process
MTP Mechanism & Kinetic
MTP Catalysts
Coke and Deactivation of Catalyst
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MTP Process
Fixed Beds[3]
: Simple in construction
Easy operating
Minimum scale-up and catalyst activity studies
Minimum regeneration cycles
Fluidized bed[4] :Alwahabi et al. proposed Circulating Fluidized Bed as a good
choice for the MTO process because of :
Excellent heat transfer properties of a fluidized bed permit
direct steam generation in coils immersed in the reactor.
Constant quality because of Continuous regeneration of the
catalyst and uniform bed temperature.
Transient temperature profiles are also uniform and stable.
The specific throughput in a fluid-bed system is higher.
Specific investment cost is lower.
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In a CFB reactor, Catalyst experiences a fast coking stage. The
fast deactivation accompanying a high exothermicity of reaction
has become the chief consideration to select reactor .
the relatively low methanol conversion after a single pass with
notable catalyst attrition, including the high investment for
scaling up the reactor, are the primary disadvantages [5].
MTP Process
Mobil
Uhde
Lurgi
Liquid Fuels Trust
Board (LFTB)
Fluidized Bed
Fixed Bed
The first MTP plant was established in China in 2010 and it
has an annual production capacity of 500,000 ton [5].
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Mechanism
Main
Mechanism
Types [6]
A consecutive-type mechanism: ethylene
will be first formed in the reaction.A hydrocarbon pool-type mechanism: Dahl
& Kolboe proposed that olefin synthesis
occurs through a carbonaceous species of
unknown stoichiometry, possibly a carbonium
ion.
Polyalkylated aromatics
Large alkylated olefins
Carbonium ions [5]
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Salehirad and Anderson by means of NMR techniquerevealed that at low loading (up to one methanol per acidsite) the methanol adsorbed in two hydrogen bondedconfigurations. At higher coverage, methanol may clusterwith the involvement of one methoxonium ion [6].
Mechanism
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Kinetic
Because the experiments was carried out at 450 Hydrocarbon
pool theory does not represent the activation energies of each
steps, so this work could not be useful for conceptual reactor
design for MTO process at different Temperatures [7].
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The equilibrium constant (K) of Reaction 1 calculated fromexperimental relationship found by Gayubo et al. over ZSM-5
catalyst as follows:
Kinetic
Chen et al. Deduced an elaborate coking model where the
coking rate equation is obtained. In addition, Chen et al.'s
simulation results were in good agreement with the actual data
[8].
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Kinetic
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Catalyst
Molecular sieves ( Zeolites, SAPO, ) are a suitable choice
for MTO reaction.
Porous structure
Concentration acid site
External surface
Unblocked sites
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high selectivity to light paraffine (mainly propane) can also be
obtained with small-pore size zeolites. Decreasing the
concentration of strong acid sites, which are responsible for
hydrogen transfer reactions, is a key factor in reducing the
conversion of olefins into paraffine.
The methods used to reduce the concentration of strong acid
sites on zeolites are dealumination, cation exchange and
isomorphous substitution of aluminium by other trivalent
cations.
Concentration acid site [10]:
Catalyst
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Catalyst
The ratio between the number of acid sites in the external surface
and those located on the intracrystalline pore surface plays an
important role in this reaction. smaller the crystallite size, the
higher this ratio.
External surface [10]:
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Catalyst
When methanol initially reaches the catalyst bed there is no
hydrocarbon pool present, but within a very short time an
active hydrocarbon pool is created and full conversion of
methanol is achieved. With an increasing time on stream, thecatalyst deactivates due to coking and the active hydrocarbon
pool moves downstream leaving deactivated catalyst behind.
unblocked sites [5]:
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Zeolites
Zeolites consist of a frame work built of tetrahedral.
Each Tetrahedron comprises a T-atom bound to four O atoms.
Oxygen bridges connect the tetrahedral.
T-atoms are Si or Al.
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Zeolites
The ERI, LTA and UFI zeolites with 8MR pore entrances also
show high selectivity for the lower olefins in the MTO. but
they deactivate rapidly in the order of LTA < ERI < UFI . the
CHA catalyst have showed a stable conversion [11].
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Increasing the selectivity to light olefins :
(1) Modification of the reaction conditions with respect to
those of the MTG process, by co-feeding water, increasing
temperature, decreasing pressure or diluting oxygenates with
an inert Gas.(2) Modification of the zeolites
Increasing its shape selectivity
Increasing hydrothermal stability
Reducing the number and strength of acid sites
Zeolites
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Catalysts of small pore size with pore openings made up
of rings of eight units (chabazite, erionite, ZSM-34,
offretite, T zeolite, and so on) is selective for MTO .
MOR zeolites, regardless of their acid site density, are highly
active and selective for the lower olefins at the initial time.
However, their deactivation rates vary considerably according
to their acid site density [12].
Zeolites
Increasing its shape selectivity
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Reducing the number and strength of acid sites:
High Si/Al ratio of zeolite leads to high ratio of propene to ethene
in products of methanol reaction.
Various catalysts such as ZSM-5 zeolites modified with phosphorus
and ferro silicalite have shown high selectivity to lower olefins in
the MTO reactions [11].
Park et al. Prepared the MOR zeolite with a lower acid site density
by careful removal of aluminum atoms from its framework which
shows slow deactivation and high selectivity for the lower
olefins[12].
Zeolites
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Increasing hydrothermal stability:
A large number of the modifications of the zeolite structure
mentioned above also serve to increase hydrothermal stability,
which does not suffice in view of the severe conditions of high
temperature and high water content in the reaction medium required
for the MTO process in order to attain high values of activity and
selectivity to olefins and to reduce deactivation by coke [13].
Zeolites
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HZSM-5 zeolite shows a moderate deactivation by coke in
the MTO process, it suffers from irreversible deactivation (by
dealuminisation) under the operating conditions.
The incorporation of Ni in the HZSM-5 zeolite implies a
decrease in total acidity and in the acid strength of the
zeolite. Consequently, the activity of the catalyst
decreases. The catalysts with Ni are hydrothermally more
stable than the parent zeolite catalyst, and activity is
completely recovered in the operation under reaction
regeneration cycles [14] .
Zeolites
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SAPOs
Alumino-Phosphate ( AlPO4)
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SAPOs
Sastre et al. found that If the siliconcontent is such that island formation
is promoted, the acidic character will
become strongly dependent on the
topology of the material. Acidity
directly relates to the concentration of
the Si island. Large proportions of
silicon-rich regions were found in
mesoporous SAPOs [6].
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Silicoaluminophosphate materials (SAPO) have a mild acidity
and, therefore, they present a very interesting alternative to obtain
high selectivity towards light olefins in the MTO process [15].
Chen et al. have Concluded that SAPO-18 and SAPO-34
which have higher acidity and cages smaller than those of
SAPO-5 and 17, exhibit high activity and selectivity
towards light olefine [16].
SAPOs
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SAPO-34SAPO-34 is an analogue to chabazite, it has nearly spherical cages linked
throughout the structure by 8-ring windows (diameter cage 4 A). In SAPO-34
silicon only substitutes for phosphorus [16].
SAPO-34 often suffers rapid deactivation although activity is completely recovered
subsequent to combustion of coke with air [13]. it also shows higher hydrothermal
stability than ZSM-5s [14].
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Effects of intracrystalline diffusion on the reactions over SAPO-34 [17].
The selective and stable catalytic performance of the CHA compared to UFI
and LTA catalystsin the MTO reaction can be explained by its cages being ofsuitable shape and size to preserve stably the active intermediates, multialkyl
benzenes, in them [11].
SAPO-34
The UOP/Hydro MTO process employs a Ni/SAPO-34 molecular sieve as a
catalyst and achieves a high yield of the lower olefins of more than 85% [12].
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SAPO-18
The structure of SAPO-18 is closely related to , but crystallographically distinct
from SAPO-34. size and shape of cages for both SAPO-18 and SAPO-34 are very
similar. Since SAPO-18 is expected to have a good performance for MTO . In
SAPO-18 silicon substitutes for both AL and P ( the amount of substituted of P is
larger than of the substituted AL)[16].
The kinetic modelling of the MTO process is studied on a SAPO-18 catalyst, which
is an interesting alternative to SAPO-34, given that it has the following advantages:
coke deactivation is significantly slower, its preparation method is simpler and the
organic template is cheaper [13,18].
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Template of SAPO synthesisThe template exerts a significant influence on both the structures and
properties of the molecular Sieves [19].
Some years ago, Vomscheid et al. demonstrated that, in the synthesis of
SAPO- 34 with morpholine and TEAOH, the importance of the template
appears not only in its role of directing the structure but also of governing
the distribution of Si in the framework, which clearly affects the catalytic
properties of the samples [9].
Ye et al. concluded that the nature of the template used in the synthesis
determines the morphology of final crystals because it influences the rate of
crystal growth [9].
SAPO-34 can be synthesized using organic amines as templates, such as
tetraethylammonium hydroxide ,isopropylamine ,dipropylamine ,piperidine
,morpholine (MOR) ,triethylamine (TEA) ,diethylamine (DEA) ,and
mixtures thereof.
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Template of SAPO synthesis
A comparative study revealed the DEA templated sample to
have the highest crystallinity and silicon content. MOR had
the second highest, and TEA the Lowest [19].
The mixed templates have also been used in the synthesis
of SAPO-34 .Jun et al. usedn morpholine and TEAOH to
synthesize SAPO-34, and foud that compared with the
SAPO-34 prepared with single template, the lifetime of the
catalyst prepared with the mixture template of 75%
morpholine and 25% TEAOH could significantly be
extended [15].
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The gel compositions and structure phases of prepared samples [15]
Template of SAPO synthesis
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REFERENCE
[1] http://en.wikipedia.org/wiki/Propene
[2] Ji Won Park et al., Applied Catalysis A: General 356 (2009) 180188[3] Frerich J. Keil, Microporous and Mesoporous Materials 29 (1999) 4966[4] Ya-Qing Zhuang et al, Powder Technology xxx (2012) xxxxxx, in press.[5] Uffe V. Mentzel et al., Applied Catalysis A: General 417418 (2012) 290297[6] Zhongmin Liu et al, Current Opinion in Solid State & Materials Science 4 (1999)80-84
[7] Ali Taheri Najafabadi et al., Journal of Industrial and Engineering Chemistry 18(2012) 2937[8] Ya-Qing Zhuang et al, Powder Technology xxx (2012) xxxxxx, in press.[9] Teresa lvaro-Munozet al., Catalysis Today 179 (2012) 2734[10] Michael Stocker, Microporous and Mesoporous Materials 29 (1999) 348[11] Ali A. Rownaghi et al., Microporous and Mesoporous Materials 151 (2012) 26
33[12] Ji Won Park et al., Applied Catalysis A: General 349 (2008) 7685
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REFERENCE
[13] Andres T. Aguayo et al., Applied Catalysis A: General 283 (2005) 197207
[14] B. Valle et al., Catalysis Today 106 (2005) 118122[15] Pengfei Wang et al., Microporous and Mesoporous Materials 152 (2012) 178184.[16] Chen et al.,Studies in Surface Science and Catalysis 84 (1994) 1731-1738[17] De Chen et al., Microporous and Mesoporous Materials 29 (1999) 191203[18] A.G. Gayubo et al., Catalysis Today 106 (2005) 112117[19] LIU Guangyu et al., Chines Journal of Catalyst 33(2012) 174-182
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