U.S. patent application number 13/553425 was filed with the patent office on 2012-12-06 for method and reactor for performing fischer-tropsch synthesis.
Invention is credited to Christophe DUWIG, Poul Erik HOJLUND NIELSEN, Max THORHAUGE.
Application Number | 20120308442 13/553425 |
Document ID | / |
Family ID | 40513763 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120308442 |
Kind Code |
A1 |
DUWIG; Christophe ; et
al. |
December 6, 2012 |
METHOD AND REACTOR FOR PERFORMING FISCHER-TROPSCH SYNTHESIS
Abstract
Method and reactor for performing Fischer-Tropsch (FT) synthesis
with controlled steam partial pressure by introducing cool points
in the FT reactor, typically in form of cooled solid surfaces. At
the surface, the low temperature will force condensation of the
water into a liquid film. Thereby, the partial pressure of steam in
the gas and reactor will not exceed significantly the vapour
partial pressure at the liquid film and water from the gas stream
will be removed as it is produced, i.e. steam induced deactivation
is avoided. In addition, the decrease of hydrogen and carbon
monoxide partial pressures due to dilution by steam will be kept
low ensuring a constant high reaction rate.
Inventors: |
DUWIG; Christophe; (Malmo,
SE) ; NIELSEN; Poul Erik HOJLUND; (Fredenborg,
DK) ; THORHAUGE; Max; (Herlev, DK) |
Family ID: |
40513763 |
Appl. No.: |
13/553425 |
Filed: |
July 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12809016 |
Jun 17, 2010 |
8258194 |
|
|
PCT/EP2009/000973 |
Feb 12, 2009 |
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13553425 |
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Current U.S.
Class: |
422/198 |
Current CPC
Class: |
B01J 2208/00141
20130101; C10G 2/341 20130101; C10G 2300/4006 20130101; B01J
2208/00123 20130101; C10G 2/34 20130101; B01J 8/067 20130101; C10G
2300/4056 20130101; B01J 2208/00115 20130101; B01J 8/0285 20130101;
B01J 2208/0015 20130101; B01J 2208/00132 20130101 |
Class at
Publication: |
422/198 |
International
Class: |
B01J 8/02 20060101
B01J008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2008 |
DK |
PA 2008 00260 |
Feb 25, 2008 |
DK |
PA 2008 00261 |
May 8, 2008 |
DK |
PA 2008 00652 |
Claims
1-6. (canceled)
7. A reactor for performing Fischer-Tropsch (FT) synthesis by
reacting a synthesis gas containing hydrogen, carbon monoxide and
carbon dioxide in a fixed bed of FT synthesis catalyst particles
indirectly cooled with a cooling agent, and condensing water as it
is prepared on a cooling surface by adjusting pressure of the
cooling agent to provide a boiling point (TBW) of the cooling agent
between 50.degree. C. and 190.degree. C., the reactor comprising,
within a common shell, the fixed bed of FT catalyst particles and
cooling means adapted to indirectly cooling the FT synthesis gas
with the cooling agent, wherein ratio of settled catalyst bulk
volume to cooling surface area of the cooling means (VCAT/ACOOL) is
between 0.01 m and 0.125 m.
8. A reactor for performing Fischer-Tropsch (FT) synthesis by
reacting a synthesis gas containing hydrogen, carbon monoxide and
carbon dioxide in a fixed bed of FT synthesis catalyst particles
indirectly cooled with a cooling agent, and condensing water as it
is prepared on a cooling surface by adjusting pressure of the
cooling agent to provide a boiling point (TBW) of the cooling agent
between 50.degree. C. and 190.degree. C., wherein at least part of
the catalyst temperature is maintained above dew point of the water
by adjusting area of the cooling surface ACOOL at the provided
boiling point of the cooling agent in such way that the ratio of
settled catalyst bulk volume (VCAT) to the cooling surface area
(ACOOL) is between 0.01 m and 0.125 m, and wherein temperature of
the FT catalyst particles is maintained above the dew point of
water by a heating agent including pressurized water with a boiling
point between 180.degree. C. and 280.degree. C., steam with a dew
point between 180.degree. C. and 280.degree. C. or a mixture
thereof, the heating agent being passed through an internal heating
means having a surface area so that ratio of the surface of heating
means to the surface of the cooling area is between 0.3 and 3.0,
the reactor comprising, within a common shell, a fixed bed of
methanol catalyst particles and cooling means adapted to indirectly
cooling the FT synthesis gas with the cooling agent and heating
means adapted to indirectly maintaining temperature of the FT
catalyst with the heating agent, wherein surface ratio of the
surface of the heating means to the cooling means (VCAT/ACOOL) is
between 0.3 and 3.0.
9. A reactor according to claim 7, further comprising internal film
stabilizing equipment adjacent to surface of the cooling means.
10. A reactor for performing Fischer-Tropsch (FT) synthesis by
reacting a synthesis gas containing hydrogen, carbon monoxide and
carbon dioxide in a fixed bed of FT synthesis catalyst particles
indirectly cooled with a cooling agent, and condensing water as it
is prepared on a cooling surface by adjusting the temperature of
the liquid cooling agent between 50.degree. C. and 190.degree. C.,
the reactor comprising, within a common shell, the fixed bed of FT
catalyst particles and cooling means adapted to indirectly cooling
the FT synthesis gas with the cooling agent, wherein ratio of
settled catalyst bulk volume to cooling surface area of the cooling
means (VCAT/ACOOL) is between 0.01 m and 0.125 m.
11. A reactor according to claim 8, further comprising internal
film stabilizing equipment adjacent to surface of the cooling
means.
12. A reactor according to claim 10, further comprising internal
film stabilizing equipment adjacent to surface of the cooling
means.
Description
[0001] This is a divisional of application Ser. No. 12/809,016,
filed Jun. 17, 2010, now U.S. Pat. No. 8,258,194, which is a 371 of
International Application No. PCT/EP2009/000973, filed Feb. 12,
2009, which claims priority to Danish Application Nos. PA2008 0260,
filed Feb. 25, 2008, PA2008 00261, filed Feb. 25, 2008, and PA2008
00652, filed May 8, 2008.
[0002] The Fischer-Tropsch (FT) process requires a synthesis gas
stream consisting largely of carbon monoxide and hydrogen. Thus,
gasification is the first step of coal liquefaction or production
of Fischer-Tropsch fuels from biomass. By the process the synthesis
gas is converted into higher hydrocarbons, carbon dioxide and
water.
[0003] Traditional FT reactors operate as fixed bed or gas agitated
reactors (slurries). Because of a better temperature control, hence
potential optimization of the product quality, slurry reactors are
a very popular choice. In addition, modern FT-catalysts based on
cobalt or ruthenium has shown good capability of forming long
carbon chain molecules (typically more than 5 carbon atoms).
[0004] The FT synthesis is exothermic and reaction performance
depends highly on the reaction temperature. High temperatures
favour formation of methane and carbon deposition on the catalyst.
It is therefore necessary to control the temperature and remove
excessive from the reaction medium, which conventionally is
accomplished by indirect heat exchange with a cooling medium in the
reactor.
[0005] Despite of the progresses mentioned above, the FT reactors
still suffer from limitations, the major one resulting from the
sensitivity of any FT catalyst to steam. Indeed, the FT reactions
forms one molecule of water per molecule of carbon monoxide
converted. Since long chain hydrocarbons are the desired reaction
product, it results in a significant increase of the steam
concentration with potential impact on the catalyst activity.
Deactivation of the FT catalyst induced by steam imposes to limit
the partial pressure of steam, typically below .about.6 bars and
preferably far below. This is conventionally done by limiting the
conversion (i.e. the water production) per flow through the
reactor. At operating pressure .about.20-30 bars, the carbon
conversion per pass would not exceed 50% which requires a
significant recycle stream and a reactor dimensioned accordingly
i.e. larger than what would be needed given the catalyst activity
only.
[0006] It has now been found that the reactor conversion rate (per
kg/catalyst) in the known FT process may be increased and the
reactor size reduced significantly, if the recycle stream is
avoided by keeping the steam partial pressure low enough and the
catalytic activity adequate.
[0007] In order to control the steam partial pressure, we suggest
introducing cool points in the FT reactor, typically in form of
cooled solid surfaces. At the surface, the low temperature will
force condensation of the water into a liquid film.
[0008] Therefore the partial pressure of steam in the gas and
reactor will not exceed significantly the vapour partial pressure
at the liquid film and water from the gas stream will be removed as
it is produced i.e. we limit the steam induced deactivation. In
addition, the decrease of hydrogen and carbon monoxide partial
pressures due to dilution by steam will be kept low ensuring a
constant high reaction rate.
[0009] In accordance with above findings, the present invention is
a method of performing Fischer-Tropsch synthesis comprising the
steps of reacting a synthesis gas containing hydrogen, carbon
monoxide and carbon dioxide in a fixed bed reactor of FT synthesis
catalyst particles being indirectly cooled with a cooling agent,
and
condensing water as it is formed in the reactor on a cooling
surface by adjusting the liquid cooling agent to provide a
temperature between 50.degree. C. and 190.degree. C.
[0010] To achieve efficient water condensation at the cold area and
adequate heat removal from the catalytic bed, different approaches
can be used. However, all possible configurations will consist of
inserting an ensemble of cooled surfaces in the reactor(s) ensuring
that any catalytic region will be in the vicinity of a cooled
surface. For example, one might pack the catalyst particles into
narrow tubes which are surrounded on the outside by a cooling agent
and a high flow of synthesis gas is passed through the tubes.
Alternatively, one may use a packed bed reactor with internal
elements in which the cooling agent circulates. These elements can
have various shapes as long as they provide adequate cooling and
ensure that any catalytic region will be in the vicinity of a
cooled surface.
[0011] The operating pressure and temperature in the reactor
(relatively far from the cool surfaces) should be kept in a range
so that the catalytic activity is adequate for enabling high
conversion.
[0012] Catalysts mostly employed in industrial FT plants and
suitable for use in the invention are metal based; typically iron,
ruthenium or cobalt based catalysts. Although iron has been widely
used in the past, modern catalysts are often based on cobalt and
show the best performances in term of selectivity.
[0013] Depending on the particular catalyst, the process can be
performed either at low or high temperature process. When using an
iron based catalyst high operating temperatures of 300-350.degree.
C. may be chosen and lower operating temperatures of
200-240.degree. C. with either an iron or a cobalt catalyst.
[0014] Fixed bed reactors are appropriate for operating
temperatures in the range of 180-350.degree. C.
[0015] The total operating pressures may vary between about 1 MPa
and 6 MPa. When employing an iron based catalyst, high pressures
are preferred as the productivity of that catalyst increases with
the operating pressure. However, one may choose an adequate
operating pressure given the catalyst activity, the cost of the
reactor and the maximum allowed steam partial pressure. Therefore,
fixing the operating pressure, it is required that the temperature
of the cool points is low enough at a given total operating
pressure to ensure condensation of the steam.
[0016] Indeed, the surface area of the cool points and their
temperature control the condensation rate which should balance the
water production rate by the FT synthesis. However, the heat losses
at the cool points should be balanced by the heat release of the FT
reactions keeping the reactor temperature steady as reactions
proceed. The temperature difference between the liquid film (cold
for enabling condensation) and the reactor (hot to maintain rapid
reactions) is sustained by the heat of reaction and condensation. A
non-dimensional criterion summarizing these balances is presented
in the following section.
[0017] In an embodiment of the invention, at least part of the
catalyst temperature is maintained above dew point of the water by
adjusting area of the cooling surface (ACOOL) at the provided
temperature of the cooling agent in such way that the ratio of
settled catalyst bulk volume (VCAT) to the cooling surface area
(ACOOL) is between 0.01 m and 0.125 m.
[0018] In further an embodiment of the invention, the temperature
of the FT catalyst particles is maintained above the dew point of
water by a heating agent including pressurized water with a boiling
point between 180.degree. C. and 280.degree. C., steam with a dew
point between 180.degree. C. and 280.degree. C. or a mixture
thereof. The heating agent is passed through an internal heating
means having a surface area so that ratio of the surface of heating
means to the surface of the cooling area is between 0.3 and
3.0.
[0019] Preferably, the average temperature of the cooling agent is
between 100.degree. C. and 180.degree. C. and the ratio of settled
catalyst bulk volume (VCAT) to the cooling surface area (ACOOL) is
between 0.01 m and 0.125 m.
[0020] The average temperature is defined as the cooling agent
temperature after having received half of the total transferred
heat.
[0021] Furthermore, the invention provides a reactor being useful
in the above described method for performing FT synthesis.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a plot of the partial pressure of different
species as a function of the carbon conversion for a first example
of the invention.
[0023] FIG. 2 is a plot of the partial pressure of different
species as a function of the carbon conversion for a second example
of the invention
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] In one embodiment the reactor comprises within a common
shell a fixed bed of FT catalyst particles and cooling means
adapted to indirectly cooling a FT synthesis gas with a cooling
agent, wherein ratio of settled catalyst bulk volume to cooling
surface area of the cooling means (VCAT/ACOOL) of the cooling means
is between 0.01 m and 0.125 m, at a temperature of the cooling
agent between 50.degree. C. and 190.degree. C.
[0025] In a further embodiment the reactor comprises within a
common shell a fixed bed of a methanol catalyst particles and
cooling means adapted to indirectly cooling a FT synthesis gas with
a cooling agent and heating means adapted to indirectly maintaining
temperature of the FT catalyst with a heating agent, wherein
surface ratio of the surface of the heating means to the cooling
means (VCAT/ACOOL) is between 0.3 and 3.0.
[0026] In still an embodiment the reactor further comprises
internal liquid film stabilizing equipment adjacent to surface of
the cooling means. Liquid film stabilizing equipment is used in
order to avoid entrainment of the condensed water into the catalyst
bed, and is installed between the catalyst and the cooling surface.
The preferred liquid film stabilizers are selected from a wire
mesh, a metal spiral, a metal helix, a porous fibre mat,
longitudinal finned cooling surface.
[0027] In order to present a criterion, we will estimate and
compare rates (production, transport, etc.) in the reactor.
[0028] The terms involved are:
[0029] The condensation rate at the cool points is
Rcond.about.k(Y-Y*) where
[0030] k is a transport coefficient,
[0031] Y denotes the mass fraction of H.sub.2O, and
[0032] * stands for vapour variables defined as in equilibrium with
the liquid film.
[0033] The heat release Hrelease.about.Hr where
[0034] H is the enthalpy of reaction, and
[0035] r is the production rate of H.sub.2O.
[0036] If all water produce is condensed at the wall, we have
Hrelease.about.Hk(Y-Y*). Indeed, this relation can be obtained by
adjusting the cooling surface area and catalyst volume
independently for a given catalytic activity.
[0037] The heat losses at the wall/film are Hlosses.about.k Cp
(T-T*), where T and T* denotes the temperature in the gas and in
the liquid film, respectively.
[0038] We define A comparing the heat release and heat losses:
A.about.(H(Y-Y*))/(Cp(T-T*)). We require A>1 for avoiding
excessive cooling.
EXAMPLE 1
[0039] In a reactor operating at P=20 bar with an averaged
temperature in the catalyst bed of T=210.degree. C. fed and a
hydrogen/carbon monoxide mixture having H.sub.2/CO=2, the cooled
surface temperature was set at 147.degree. C. The reactants are
converted by:
CO+2H.sub.2->CH.sub.2+H.sub.2O
[0040] CH.sub.2 reacts further to produce long carbon chain
molecules. The reaction is exothermic (enthalpy of reaction is
-H=-165 kJ/mol), while the calorific capacity of the mixture varies
with the carbon conversion in the range Cp.about.30-50 J/mol/K.
[0041] FIG. 1 of the drawings plots the partial pressure of
different species as function of the carbon conversion. At
conversions lower than 0.5, the partial pressures vary linearly
with the conversion, water is produced and accumulates in the gas
phase as reactants are consumed. At conversion -0.5, the film
condensation start and the partial pressure of water stabilizes at
4.5 bars below the upper limit (taken here to be .about.6 bars).
Reaction proceeds to almost complete conversion keeping the
reactant partial pressures high and constant. For this case, we
estimate the non-dimensional number A to be A.about.1.3 at
conversion 0.5 and increasing as reaction proceeds in the reactor
so that the catalyst temperature is suitable for FT synthesis.
EXAMPLE 2
[0042] In a reactor operating at P=35 bar with an averaged
temperature in the catalyst bed of T=210.degree. C. fed and a
hydrogen/carbon monoxide mixture having H.sub.2/CO=2, the cooled
surface temperature was set at 155.degree. C. The reactions are
similar than in Example 1.
[0043] FIG. 2 of the drawings plots the partial pressure of
different species as function of the carbon conversion. At
conversions lower than 0.4, the partial pressures vary again
linearly with the conversion, water is produced and accumulates in
the gas phase as reactants are consumed. At conversion .about.0.4,
the film condensation start and the partial pressure of water
stabilizes at 5.7 bars below the upper limit (also taken here to be
-6 bars). Reaction proceeds to almost complete conversion keeping
the reactant partial pressures high and constant. For this case, we
estimate the non-dimensional number A to be A.about.1.3 at
conversion 0.4 and increasing as reaction proceeds in the reactor
so that the catalyst temperature is suitable for FT synthesis.
[0044] The advantages of the condensing reactor compared to
conventional techniques are:
[0045] Remove the recycle stream and lowers the size of the
equipment (both compressor and reactor) i.e. the erection
costs.
[0046] Decrease the water content of the gas phase, which allows
operations at higher pressures/catalytic activities or/and maintain
a relatively constant reactant partial pressures in the
reactor.
[0047] The removal of water also decreases the gas flow velocity
reducing the pressure drop per unit length significantly in the
region of high conversion. It allows using small catalyst
particles, the intra particle diffusion limitation decreases as the
reactivity increases, while keeping the pressure drop
reasonable.
[0048] Without recycle loop, there is no accumulation of inert
species and the demand on synthesis gas composition are lower i.e.
the synthesis gas preparation can be simplified (cost-reduced)
without significant loss of conversion efficiency.
* * * * *