Methanol to Prop y Lene

7/30/2019 Methanol to Prop y Lene

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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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http://en.wikipedia.org/wiki/Propenehttp://en.wikipedia.org/wiki/Propene


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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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Methanol to Prop y Lene

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