Wednesday, May 7, 2014
Friday, March 21, 2014
QUESTIONS AND ANSWERS
I FLUID CATALYTIC CRACKING: www.wissenschaftler-avh.in
B.CATALYST/ADDITIVES(Contd.)
Q.54: Give a Brief introduction to FCC Additives.
A.54:
Tuesday, January 21, 2014
QUESTIONS AND ANSWERS
I.FLUID CATALYTIC CRACKING: www,wissenschaftler-avh.in
B.CATALYST/ADDITIVES(Contd.):
Q-53
How Heavy Metals contaminate the FCC Catalyst?
A-53
Heavy Metal contamination on FCC Catalyst
All cat cracker feedstock contain heavy metal contaminantsin the ppm range, the most common metals being nickel (Ni),vanadium (V), iron (Fe) and copper (Cu), all of which promote dehydrogenation and condensation reactions.
Extensive investigation of their relative activity for coke and hydrogen production indicate that nickel is four times as active as vanadium (4Ni + V) in producing hydrogen and coke[1] as studied by Arco back in the 1970s. Iron was not considered significant since this metal is usually present as “tramp” iron and is not catalytically active.
A distinction must be made between tramp Fe and Fe deposited on the cracking catalyst. Tramp Fe is composed of Fe particles in the catalyst stream that originate from erosion of pipes, vessels and other hardware. To the extent that these particles do not break up in very fine particles that can attach
themselves to the cracking catalyst, they have little effect on catalyst activity and selectivity. However, they could affect CO oxidation and SOx emissions. Iron deposited on the catalyst is in most cases the result of organic, colloidal or other finely dispersed Fe in feed. It has been recently recognized that this latter form of Fe is an important factor causing FCC catalyst deactivation. Most often, loss of activity and bottoms
cracking has been observed. Decreases in average bed density (ABD) have also been reported. In general, the more finely dispersed the depositing Fe is, the more effective it is in causing catalyst deactivation. Fe compounds present in crude oil, and as minute impurities in cracking catalyst, have some dehydrogenation activity but at orders of magnitude less than Ni or V.
Grace Davison generally uses a catalyst Ni equivalent index of Ni + Cu + V/4, which assumes that Cu and Ni are equal in dehydrogenation activity. It should be noted that an NPRA paper dating back to 1979 by Ashland /UOP has indicated the Ni or V equivalent factors may not be accurate in assessing the relative contribution of metals, especially at high concentrations, because of a non-linear response of the ontaminants. It should be stressed that the previously noted Ni equivalent indices do not necessarily reflect the relative
effects on catalyst activity, but rather only the effects on coke and gas make.
Gas Production & Compressor Limits
Both pilot plant and commercial data have shown a number of undesirable yield shift changes occurring as metals accumulate on the catalyst. The most obvious result of metals poisoning is a sharp increase in hydrogen production. Although the wt% increase is not usually significant, the volume of gas can
rise dramatically and limit compressor capacity A common means of tracking H2 make is via the H2/C1,
or H2/(C1 + C2) molar ratio. With this method the ratio remains fairly constant with conversion as long as reactor temperature and feedstock remain constant, so changes should reflect differences in metal activity. A relatively metals-free commercial operation may operate with a 0.2-0.3 H2/CH4 ratio, whereas resid operations encounter ratios well above 1.0. Levels up to 3.0 have been reported to Grace Davison.
At typical FCC catalyst addition rates, less than one-third of the total metals on commercial equilibrium catalyst are active dehydrogenation catalysts themselves. It should be understood that the activity of metals deposited on the catalyst in a commercial FCCU is much less than an equal amount of artificially deposited metals due to the passivation effect brought about by the continuous reaction regeneration cycles
encountered in the commercial unit Concurrent with the increased hydrogen, metals increase contaminant coke yield. The metals that catalyze H2 formation also catalyze condensation/polymerization reactions,which form coke. .
B.CATALYST/ADDITIVES(Contd.):
Q-53
How Heavy Metals contaminate the FCC Catalyst?
A-53
Heavy Metal contamination on FCC Catalyst
All cat cracker feedstock contain heavy metal contaminantsin the ppm range, the most common metals being nickel (Ni),vanadium (V), iron (Fe) and copper (Cu), all of which promote dehydrogenation and condensation reactions.
Extensive investigation of their relative activity for coke and hydrogen production indicate that nickel is four times as active as vanadium (4Ni + V) in producing hydrogen and coke[1] as studied by Arco back in the 1970s. Iron was not considered significant since this metal is usually present as “tramp” iron and is not catalytically active.
A distinction must be made between tramp Fe and Fe deposited on the cracking catalyst. Tramp Fe is composed of Fe particles in the catalyst stream that originate from erosion of pipes, vessels and other hardware. To the extent that these particles do not break up in very fine particles that can attach
themselves to the cracking catalyst, they have little effect on catalyst activity and selectivity. However, they could affect CO oxidation and SOx emissions. Iron deposited on the catalyst is in most cases the result of organic, colloidal or other finely dispersed Fe in feed. It has been recently recognized that this latter form of Fe is an important factor causing FCC catalyst deactivation. Most often, loss of activity and bottoms
cracking has been observed. Decreases in average bed density (ABD) have also been reported. In general, the more finely dispersed the depositing Fe is, the more effective it is in causing catalyst deactivation. Fe compounds present in crude oil, and as minute impurities in cracking catalyst, have some dehydrogenation activity but at orders of magnitude less than Ni or V.
Grace Davison generally uses a catalyst Ni equivalent index of Ni + Cu + V/4, which assumes that Cu and Ni are equal in dehydrogenation activity. It should be noted that an NPRA paper dating back to 1979 by Ashland /UOP has indicated the Ni or V equivalent factors may not be accurate in assessing the relative contribution of metals, especially at high concentrations, because of a non-linear response of the ontaminants. It should be stressed that the previously noted Ni equivalent indices do not necessarily reflect the relative
effects on catalyst activity, but rather only the effects on coke and gas make.
Gas Production & Compressor Limits
Both pilot plant and commercial data have shown a number of undesirable yield shift changes occurring as metals accumulate on the catalyst. The most obvious result of metals poisoning is a sharp increase in hydrogen production. Although the wt% increase is not usually significant, the volume of gas can
rise dramatically and limit compressor capacity A common means of tracking H2 make is via the H2/C1,
or H2/(C1 + C2) molar ratio. With this method the ratio remains fairly constant with conversion as long as reactor temperature and feedstock remain constant, so changes should reflect differences in metal activity. A relatively metals-free commercial operation may operate with a 0.2-0.3 H2/CH4 ratio, whereas resid operations encounter ratios well above 1.0. Levels up to 3.0 have been reported to Grace Davison.
At typical FCC catalyst addition rates, less than one-third of the total metals on commercial equilibrium catalyst are active dehydrogenation catalysts themselves. It should be understood that the activity of metals deposited on the catalyst in a commercial FCCU is much less than an equal amount of artificially deposited metals due to the passivation effect brought about by the continuous reaction regeneration cycles
encountered in the commercial unit Concurrent with the increased hydrogen, metals increase contaminant coke yield. The metals that catalyze H2 formation also catalyze condensation/polymerization reactions,which form coke. .
Monday, January 20, 2014
QUESTIONS AND ANSWERS
I.FLUID CATALYTIC CRACKING: www.wissenschaftler-avh.in
B.CATALYST/ADDITIVES(Contd.)
Q-52:
Pl .Highlight the role of LOW RARE EARTH CATALYSTS in FCC operation?
A-52:
For decades, rare earth elements have performed vital roles in refinery catal-ysis and their availability, at reasonable prices, has been taken for granted. However, when the global supply became restricted, refiners faced spiral- ling costs and were forced to re-examine how they used rare earth elements.
Uses of rare earth elements
The rare earth elements are lanthanum, cerium, praseodym- ium, neodymium, promethium, samarium, europium, gadolin- ium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Yttrium and sometimes scandium are often grouped as rare earth elements because of their similar chemical properties. These elements have a widerange of industrial applications. They have taken an important role in oil refining catalysts, additives and processes for many years, and also make vital contributions to other applications. Selected end uses for rare earths are shown in Table 1.Global demand for rare earth elements is currently about 134 000 t/y, but worldwide annual production amounts to 124 000 tonnes, the difference being drawn from previously mined stocks.
However, the availability of rare earths can no longer be taken for granted. In 2009, China, the largest producer of rare earth elements,( output 97% of the world’s rare earths measured in terms of oxide content.) cut its export of rare earths from about 50 000 tonnes in 2009 to 30 000 tonnes in 2010. The country also plans to reduce output further by eliminating prohibited rare earth mining operations. This is likely to restrict the availability of rare earth elements even more. Greater emphasis by the Chinese authorities on the safety and environmental aspects of mining operations are likely to increase operating costs. The much-reduced availability of rare earths means that their price has soared. The price for lanthanum, for example, surged from some $6000/t in May 2010 to about $140 000/t in May 2011.
Selected uses of rare earth elements
Light rare earth element Major end use Heavy rare earth element Major end use Lanthanum Hybrid engines, metal alloys, refining catalysts Terbium Phosphors, permanent magnets Cerium Automotive catalysts, refining catalysts, metal alloys Dysprosium Permanent magnets, hybrid engines Praseodymium Magnets Erbium Phosphors
Neodymium Automotive catalysts, hard drives in laptops, headphones, hybrid engines Holmium Glass colouring, lasers Samarium Magnets Thulium Medical X-ray units Europium Red colouration for television and computer screens Ytterbium Lasers, steel alloys Gadolinium Magnets
Table 1 Adapted from: DOI, US Geological Survey, Circular 930-N
Laboratory comparison of two catalysts with the same formulation but with and without rare earth exchange
Catalyst no rare earth rare earth exchanged
RE2O3, wt% 0.0 1.0
Conversion at C/O = 4 wt/wt, wt% Base +6.9
Yield structure, wt%
Dry gas Base +0.90
Propane Base +0.19
Propylene Base +0.44
n-butane Base +0.15
i-butane Base +0.66
Butylenes Base +0.28
Gasoline Base +4.8
Light cycle oil Base -1.1
Bottoms Base -5.8
Coke Base +0.9
Selectivities, wt/wt
C3-olefinicity Base -0.02
C4-olefinicity Base -0.08
Gasoline/conversion Base +0.01
Coke/second order conversion Base -0.40
Table 2
This comparison at a constant catalyst-to-oil ratio (C/O)shows the typical changes through applying rare earth exchange to zeolites:• The activity is substantially increased, which results in much higher liquefied petroleum gas (LPG) and particularly, gasoline yield,mainly at the cost of bottoms
• The olefinicity of the LPG fraction is decreased • Owing to the lower olefinicity, gasoline olefinicity and octanes will also increase.• Coke and delta coke are also increased.No other elements have yet been found to increase zeolite activity and stability as efficiently as rare earth elementsThere are limited sources of rare earth elements outside China but the quantities currently produced are too low to have any significant impact on short-term supply. Initiatives are being taken in, for example,Australia, Brazil, Canada, South Africa, Greenland and the US, to find and develop new sources of rare earths or to reopen mines previously considered uneconomic. But, as demand is projected to increase from 134 000 t/y to 180 000 t/y in 2012, it is unlikely that any new rare earth production will close the widening gap in the short term,as greenfield mining projects could take 10 years to reach production.
Rare earth elements in FCC catalysts
Rare earths have found applications in oil refining for FCC catalysts and additives, which use lanthanum and cerium.Lanthanum and cerium are used in FCC catalysts because they substantially increase the activity and stability of the zeolite, which is the most active component in the catalysts.Lanthanum is most commonly used to increase the activity and stability of zeolites.The effects of lanthanum on the performance of a zeolite-containing FCC catalyst are shown in Table 2. This data was obtained from laboratory work in which two catalysts were compared in the short-contact- time riser test (SCT-RT)after a two-step cyclic metal deactivation with 5000 ppm of nickel (Ni), 5000 ppm of vanadium (V) and a residue feed stock. The catalysts have the same composition, but the first one has not been exchanged with rare earth and the second one contains 1 wt% RE2O3.
CONCLUSIONS
Rare earth elements have been of great importance to oil refiners for processing marginal feedstocks in the FCC unit, which is still the preferred unit for converting marginal feed-stocks into LPG and transportation fuels. However, soaring rare earth prices have created turmoil for the refining industry.
B.CATALYST/ADDITIVES(Contd.)
Q-52:
Pl .Highlight the role of LOW RARE EARTH CATALYSTS in FCC operation?
A-52:
For decades, rare earth elements have performed vital roles in refinery catal-ysis and their availability, at reasonable prices, has been taken for granted. However, when the global supply became restricted, refiners faced spiral- ling costs and were forced to re-examine how they used rare earth elements.
Uses of rare earth elements
The rare earth elements are lanthanum, cerium, praseodym- ium, neodymium, promethium, samarium, europium, gadolin- ium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Yttrium and sometimes scandium are often grouped as rare earth elements because of their similar chemical properties. These elements have a widerange of industrial applications. They have taken an important role in oil refining catalysts, additives and processes for many years, and also make vital contributions to other applications. Selected end uses for rare earths are shown in Table 1.Global demand for rare earth elements is currently about 134 000 t/y, but worldwide annual production amounts to 124 000 tonnes, the difference being drawn from previously mined stocks.
However, the availability of rare earths can no longer be taken for granted. In 2009, China, the largest producer of rare earth elements,( output 97% of the world’s rare earths measured in terms of oxide content.) cut its export of rare earths from about 50 000 tonnes in 2009 to 30 000 tonnes in 2010. The country also plans to reduce output further by eliminating prohibited rare earth mining operations. This is likely to restrict the availability of rare earth elements even more. Greater emphasis by the Chinese authorities on the safety and environmental aspects of mining operations are likely to increase operating costs. The much-reduced availability of rare earths means that their price has soared. The price for lanthanum, for example, surged from some $6000/t in May 2010 to about $140 000/t in May 2011.
Selected uses of rare earth elements
Light rare earth element Major end use Heavy rare earth element Major end use Lanthanum Hybrid engines, metal alloys, refining catalysts Terbium Phosphors, permanent magnets Cerium Automotive catalysts, refining catalysts, metal alloys Dysprosium Permanent magnets, hybrid engines Praseodymium Magnets Erbium Phosphors
Neodymium Automotive catalysts, hard drives in laptops, headphones, hybrid engines Holmium Glass colouring, lasers Samarium Magnets Thulium Medical X-ray units Europium Red colouration for television and computer screens Ytterbium Lasers, steel alloys Gadolinium Magnets
Table 1 Adapted from: DOI, US Geological Survey, Circular 930-N
Laboratory comparison of two catalysts with the same formulation but with and without rare earth exchange
Catalyst no rare earth rare earth exchanged
RE2O3, wt% 0.0 1.0
Conversion at C/O = 4 wt/wt, wt% Base +6.9
Yield structure, wt%
Dry gas Base +0.90
Propane Base +0.19
Propylene Base +0.44
n-butane Base +0.15
i-butane Base +0.66
Butylenes Base +0.28
Gasoline Base +4.8
Light cycle oil Base -1.1
Bottoms Base -5.8
Coke Base +0.9
Selectivities, wt/wt
C3-olefinicity Base -0.02
C4-olefinicity Base -0.08
Gasoline/conversion Base +0.01
Coke/second order conversion Base -0.40
Table 2
This comparison at a constant catalyst-to-oil ratio (C/O)shows the typical changes through applying rare earth exchange to zeolites:• The activity is substantially increased, which results in much higher liquefied petroleum gas (LPG) and particularly, gasoline yield,mainly at the cost of bottoms
• The olefinicity of the LPG fraction is decreased • Owing to the lower olefinicity, gasoline olefinicity and octanes will also increase.• Coke and delta coke are also increased.No other elements have yet been found to increase zeolite activity and stability as efficiently as rare earth elementsThere are limited sources of rare earth elements outside China but the quantities currently produced are too low to have any significant impact on short-term supply. Initiatives are being taken in, for example,Australia, Brazil, Canada, South Africa, Greenland and the US, to find and develop new sources of rare earths or to reopen mines previously considered uneconomic. But, as demand is projected to increase from 134 000 t/y to 180 000 t/y in 2012, it is unlikely that any new rare earth production will close the widening gap in the short term,as greenfield mining projects could take 10 years to reach production.
Rare earth elements in FCC catalysts
Rare earths have found applications in oil refining for FCC catalysts and additives, which use lanthanum and cerium.Lanthanum and cerium are used in FCC catalysts because they substantially increase the activity and stability of the zeolite, which is the most active component in the catalysts.Lanthanum is most commonly used to increase the activity and stability of zeolites.The effects of lanthanum on the performance of a zeolite-containing FCC catalyst are shown in Table 2. This data was obtained from laboratory work in which two catalysts were compared in the short-contact- time riser test (SCT-RT)after a two-step cyclic metal deactivation with 5000 ppm of nickel (Ni), 5000 ppm of vanadium (V) and a residue feed stock. The catalysts have the same composition, but the first one has not been exchanged with rare earth and the second one contains 1 wt% RE2O3.
CONCLUSIONS
Rare earth elements have been of great importance to oil refiners for processing marginal feedstocks in the FCC unit, which is still the preferred unit for converting marginal feed-stocks into LPG and transportation fuels. However, soaring rare earth prices have created turmoil for the refining industry.
QUESTIONS AND ANSWERS
I.FLUID CATALYTIC CRACKING: www.wissenschaftler-avh.in
B.CATALYST/ADDITIVES(Contd.)
Q-51
What are the effects of Rare Earths on FCC Catalysts
A-51
A refiner's own product requirements determine whether a rare earth or non rare earth catalyst is used. If gasoline is desired, a rare earth cracking catalyst
should be used; if higher gasoline octane
is required, a minimum rare earth catalyst
or partial rare earth catalyst
should be the catalyst choice.
For a catalyst containing reduced
levels or no rare earth,
the use of an Ultrastable (USY) Zeolite
Catalyst is recommended for improved hydrothermal stability.
B.CATALYST/ADDITIVES(Contd.)
Q-51
What are the effects of Rare Earths on FCC Catalysts
A-51
What are Rare
Earths?
Rare earth is a generic name used for the 14 metallic elements
of the Lanthanide series which contain the atomic numbers
from 57 through
71 plus Scandium (At. #21) and Yttrium
(At. #39). These elements occupy
a unique place in the periodic chart. They are the first elements
where the increasing atomic number results
in the filling of the inner electron
shell after an outer shell has been filled,
causing a high similarity in chemical properties. This similarity complicates the separation of one rare earth from another. They are, therefore, often supplied as a mixture
of oxides as extracted from ores such as bastnaesite or monazite.
The typical
rare earth consists of 46% Cerium Oxide, 20% Lanthanum Oxide, 15% Neodymium Oxide, as well as other oxides of the series.
Processors also supply
a form of rare earth
in which the greater part of the Cerium has been removed.
This mixture, known as "Lanthanum rich", contains 6-10% Ce 2O3, up to 80% La 2O3, 15% Nd 2O3 and other oxides. Extensive laboratory tests indicate minimum
difference in catalytic
performance, and FCC catalysts are accordingly treated
with either of the two mixtures.
Why Rare
Earths?
. . . Hydrothermal Stability
Lack of hydrothermal stability is the primary reason for adding rare earth oxides to catalytic cracking catalysts. Upon exposure to the high temperatures observed
in commercial FCC regenerators the original X-type zeolite cracking
catalysts had a tendency to sinter and become amorphous in nature, resulting in a loss of catalyst
activity. Addition of rare earth oxides to the cracking catalysts improved
their hydrothermal stability; providing stable operations at regenerator temperatures as high as 1300° F.
The subsequent development of Y-type zeolites
improved the catalyst's inherent hydrothermal stability. In fact, these newer FCC catalysts without rare
earth could withstand
temperatures comparable to their earlier
counterparts with rare earth. These Y-type zeolites with
rare earth remain stable at temperatures as high as 1400° F. Figure 1 illustrates differences in catalyst hydrothermal stability with and without
rare earth stability.
Higher Gasoline Yield and Reduced Gas
Make
Rare earth oxides are added to zeolite
cracking catalysts through a process
known as ion exchange. During this process a portion
of the acidic protons and sodium located within the zeolite crystal are exchanged with rare earth ions.
Because rare earth inhibits
the dealumination of a zeolite,
a higher concentration of acid sites will be found in a rare earth exchanged catalyst.
This improves both the activity and the hydrothermal stability of the catalyst. On average, these sites are weaker and in closer
proximity to each other than those found in a more highly
dealuminated catalyst characterized by lower unit cell size measurements.
As a result of the greater
number of active sites, both the primary
cracking and primary
hydrogen transfer reactions that occur within the zeolite
are enhanced. Primary
cracking reactions involve
the initial scission
of the carbon-carbon bond to form higher valued liquid products
such as gasoline. Primary hydrogen
transfer reactions are those that occur between
cracked products to terminate the cracking
reactions in the gasoline range, thus, reducing
the overcracking of gasoline to C 3's and C 4's. The hydrogen transfer reactions are greatly increased
with the addition
of rare earth to the zeolite.
Thus, rare earth in catalytic
cracking catalysts enhances their gasoline yield.
Lower Octane and Reduced Cetane Index
The addition
of rare earth into the zeolite inhibits
the degree of unit cell size shrinkage
during
equilibration in the regenerator. Steam in the FCC regenerator removes active acidic alumina from the zeolite. Rare earth inhibits the extraction of aluminum from the zeolite's structure (dealumination) which in turn increases the equilibrium unit cell size for FCC catalysts. Since reducing the equilibrium unit cell size of an FCC catalyst has the effect of improving octane, adding rare earth decreases the octane.
equilibration in the regenerator. Steam in the FCC regenerator removes active acidic alumina from the zeolite. Rare earth inhibits the extraction of aluminum from the zeolite's structure (dealumination) which in turn increases the equilibrium unit cell size for FCC catalysts. Since reducing the equilibrium unit cell size of an FCC catalyst has the effect of improving octane, adding rare earth decreases the octane.
In addition
to the above mentioned reactions, the rate of secondary hydrogen transfer reactions is also increased by rare earth. For
a rare earth
exchanged cracking catalyst
the hydrogen transfer
reaction of interest
is as follows:
Naphthenes(LCO) + Olefins(Gasoline) ->
Aromatics(LCO) + Paraffins(Gasoline)
Thus hydrogen
transfer reduces the amount of olefins found in the product. These reactions also influence the molecular weight distribution of the product by terminating carbonium
ions before they crack to shorter chain fragments. As hydrogen transfer reactions increase
relative to cracking reactions, olefin yield, light gas yield and octanes decrease, while gasoline yield increases.
Because rare earth
oxides promote hydrogen
transfer, the yield
of C 3 and C 4 olefins in the LPG fraction will be lower.
The resulting
reduction in the total LPG yield results in a reduction
in the wet gas yield. This reduction in wet gas can have a major effect on plant operations, as compressor capacity
is often the limiting factor
for FCC unit throughput.
Subscribe to:
Posts (Atom)