Molecular sieve abstract
The invention concerns a process for skeletal isomerisation of
linear olefins using a catalyst containing at least one pre-treated
molecular sieve selected from the group formed by SAPO-31 SAPO-11
Theta-1 EU-1 omega zeolite, mordenite, Nu-10 Nu-86 Nu-87 ferrierite,
ZSM-12 and ZSM-23. The pre-treatment process consists in bringing
the molecular sieve, which has a pore size of 0.4 to 0.8 nm, into
contact with at least one hydrocarbon molecule containing 4 to 20
carbon atoms, at a space velocity of 0.1-45 h.sup.-1 a temperature
of 300-550.degree. C. and at a pressure of 0.1-1 MPa, for 0.5-48
h, to deposit coke in the pores. The process is of particular application
to one-dimensional sieves. It is preferably carried out outside
the reaction zone. The invention also concerns a catalyst containing
a pre-treated sieve, the sieve being selected from SAPO-31 SAPO-11
Theta-1 EU-1 omega zeolite, mordenite, ferrierite, Nu-10 Nu-86
and Nu-87.
Molecular sieve claims
1. A process for skeletal isomerisation of a feed containing linear,
olefinic hydrocarbons containing 4 to 20 carbon atoms using a catalyst
containing at least one molecular sieve with a pore size in the
range 0.4 nm to 0.8 nm, characterized in that prior to commencing
the process, said sieve is brought into contact with at least one
hydrocarbon molecule containing 4 to 20 carbon atoms at a space
velocity of 0.1-45 h.sup.-1 a temperature of 300-550.degree. C.,
and at a pressure of 0.1-1 MPa for 0.5-48 h, to deposit coke in
said pores in said sieve.
2. A process according to claim 1 in which the hydrocarbon molecule
contains 4 to 12 carbon atoms.
3. A process according to claim 1 or claim 2 in which the hydrocarbon
molecule is selected from the group formed by monoolefins, polyolefins
and alkanes.
4. A process according to any one of the preceding claims, in which
the hydrocarbon molecule is diluted in an inert gas.
5. A process according to any one of the preceding claims, in which
the temperature is in the range 400.degree. C. to 535.degree.C.,
the pressure is in the range 0.1 MPa to 0.5 MPa, the space velocity
is in the range 0.5 h.sup.-1 to 25 h.sup.-1 and the duration is
in the range 0.5 h to 24 h.
6. A process according to claim 1 in which the sieve has a pore
size in the range 0.4 nm to 0.7 nm.
7. A process according to any one of the preceding claims, in which
the sieve includes a one-dimensional microporous network.
8. A process according to any one of the preceding claims, in which
the molecular sieve is selected from the group formed by ferrierite,
SAPO-31 SAPO-11 Theta-1 EU-1 ZSM-12 ZSM-23 omega zeolite,
mordenite, Nu-10 Nu-86 and Nu-87.
9. A process according to any one of the preceding claims, in which
the sieve is pre-treated before forming it in a matrix.
10. A process according to any one of the preceding claims, in
which the sieve is pre-treated after forming it in a matrix.
11. A process according to any one of the preceding claims, in
which the sieve is pre-treated outside the reaction zone.
12. A process according to any one of the preceding claims, in
which the feed is brought into contact with the catalyst at a temperature
of 150-500.degree. C., a pressure of 0.01-1 MPa, and at a space
velocity of 0.1-10 h.sup.-1.
13. A process according to any one of the preceding claims, applied
to olefinic C.sub.4 feed.
14. A process according to any one of claims 1 to 12 applied to
an olefinic C.sub.5 feed.
15. A catalyst containing at least one molecular sieve selected
from the group formed by ferrierite, SAPO-31 SAPO-11 Theta-1
EU-1 omega zeolite, mordenite, Nu-10 Nu-86 and Nu-87 said sieve
having been brought into contact with at least one hydrocarbon molecule
containing 4 to 20 carbon atoms at a space velocity of 0.1-45 h.sup.-1
a temperature of 300-550.degree. C. and at a pressure of 0.1-1 MPa,
for 0.5-48 h, to deposit coke in the pores of said sieve.
16. A catalyst according to claim 13 in which the sieve is brought
into contact with at least one hydrocarbon molecule selected from
the group constituted by monoolofins, polyolefins and alkanes, containing
4 to 12 carbon atoms, at a temperature of 400-535.degree. C. and
at a pressure of 0.1-0.5 MPa, in the absence of hydrogen.
17. A catalyst according to claim 15 or claim 16 in which the
sieve is pre-treated before forming it in a matrix.
18. A catalyst according to claim 15 or claim 16 in which the
sieve is pre-treated after forming it in a matrix.
Molecular sieve description
[0001] The invention concerns a process for skeletal isomerisation
of linear olefins using a sieve which has a pore size in the range
0.4 nm to 0.8 nm and which has been pre-treated by coking to render
it selective.
[0002] The invention also concerns a catalyst containing a sieve
selected from the group formed by SAPO-31 SAPO-11 Theta-1 EU-1
omega zeolite, mordenite, ferrierite, Nu-10 Nu-86 and Nu-87 which
has been pre-treated by coking to render it selective.
[0003] Processes for treatment by coking have already been described
for catalysts used for aromatic alkylation or isomerisation, or
for the oligomerisation of olefins.
[0004] U.S. Pat. No. 4508836 describes a treatment process applied
to a catalyst used to convert aromatic feeds by alkylation or isomerisation,
the catalyst containing a zeolite with a constraint index in the
range 1 to 12 particularly ZSM-5 -11 -12 -35 or -38. The treatment
described consists in bringing the catalyst into contact with an
aromatic compound (toluene), optionally in the presence of hydrogen,
at a temperature of less than 650.degree. C., to deposit more than
1% of coke.
[0005] U.S. Pat. No. 5234875 describes a catalyst used for oligomerisation
of olefins, which contains a ZSM-23 and which has been pre-coked
with an olefin, at a temperature of 200-500.degree. C. and at a
pressure of more than 27 bars.
[0006] In the present invention, oligomerisation of the olefins
(i.e., polymerisation), would reduce the yield, must be avoided.
[0007] Because of the reduction in the level of lead alkyls in
petrol over the past few years, the refiner has had to plan to incorporate
different compounds into the petrol, in particular alcohols and
ethers, to increase the octane number. In addition to methanol which
is one of the most important known additives, MTBE (methyl-tertiobutylether)
possesses antiknock properties which improve petrol quality and
increase the octane number by a greater amount than that obtained
with methanol. MTBE has other advantages, such as:
[0008] a boiling point which corresponds to that of the petrol
components with the poorest antiknock properties;
[0009] a vapour tension which is compatible with those components;
[0010] an excellent freezing point;
[0011] low solubility in water;
[0012] complete miscibility with hydrocarbons, etc.
[0013] MTBE is generally obtained from isobutene and methanol in
the following reaction: 1
[0014] Isobutene is generally contained in olefinic C.sub.3-C.sub.4
cuts from effluents from catalytic cracking, steam cracking, thermal
cracking and visbreaking. However, the quantities of isobutene produced
by these different processes are not sufficient to allow large scale
development of the MTBE production process.
[0015] For this reason, in order to produce larger quantities of
isobutene, it has been suggested that the butenes contained in the
effluents from the above processes should be completely or almost
completely isomerised.
[0016] A number of processes associated with a number of catalysts
have been proposed in the literature.
[0017] Those catalysts are generally based on alumina or on molecular
sieves.
[0018] A number of catalysts for isomerisation of olefins, more
precisely butene to isobutene, incorporate molecular sieves with
two-or three-dimensional microporous networks where the channels
are interconnected. Those sieves can be associated with a metal
"hydrogenating" function such as platinum, palladium or
gallium. The main drawbacks of this type of catalyst are:
[0019] deactivation due to the formation of a large quantity of
coke;
[0020] formation of unwanted products such as dimers and trimers
of butenes and aromatic compounds.
[0021] The term "molecular sieve" means zeolites, i.e.,
crystalline microporous aluminosilicates, which may be synthetic
or natural, also other molecular sieves such as silicoaluminophosphates,
SAPO (U.S. Pat. No. 4440871), aluminophosphates and their derivatives
with a metal integrated therein, i.e., MeAPOs and ELAPOs, also silicoaluminophosphates
with a metal integrated therein, i.e., MeAPSOs, or ELAPSOs.
[0022] More recently, it has been shown that zeolites or molecular
sieves containing a one-dimensional microporous network where the
pore opening is greater than 0.42 nm and less than 0.7 nm (European
patents EP-A-0 523 838 EP-A-0 501 577) can constitute the active
phases in catalysts for the skeletal isomerisation of linear olefins.
[0023] The structures cited in the above patents are ferrierite,
SAPO-11 and a mordenite which has been exchanged with magnesium.
[0024] During studies aimed at improving the performance of these
catalysts, it was surprisingly discovered that a molecular sieve
which preferably contained a one-dimensional microporous network
with a pore size in the range 0.4 nm to 0.8 nm which had undergone
a coking pre-treatment under precise conditions to partially or
almost completely block the microporous volume led to improved selectivity
towards iso-olefins (for example isobutene) during skeletal isomerisation
of olefins (for example n-butenes). These catalysts also have good
catalytic stabilities.
[0025] One object of the invention is to provide a skeletal isomerisation
process using a catalyst containing at least one molecular sieve
with a pore size in the range 0.4 nm to 0.8 nm, in which prior to
commencing the process, said sieve has been brought into contact
with at least one hydrocarbon molecule containing 4 to 20 carbon
atoms at a space velocity of 0.1-45 h.sup.-1 a temperature of 300-550.degree.
C. and at a pressure of 0.1-1 MPa for 0.5-48 h, to deposit coke
in said pores of said sieve.
[0026] The present invention advantageously concerns molecular
sieves with a pore size in the range 0.4 nm to 0.7 nm, and which
preferably has a one-dimensional microporous network. Non limiting
and non exhaustive examples of molecular sieves which can be treated
using the process of the invention are: ferrierite (structure type
FER), SAPO-31 SAPO-11 (structure type AEL), Theta-1 (structure
type TON), EU-1 (structure type EUO), ZSM-12 (structure type MTW),
ZSM-23 (structure type MTT), omega zeolite, mordenite, Nu-10 Nu-86
and Nu-87.
[0027] The molecular sieve is treated before (preferred) or after
forming in a matrix selected from the group which is preferably
formed by alumina, magnesia, silica-alumina and natural clays (kaolin,
bentonite), and using techniques such as extrusion, pelletization
or bowl granulation. Any matrix which is known to the skilled person
may be suitable.
[0028] The sieve can also be used as it is, without a matrix.
[0029] Elements from various groups in the periodic classification
may optionally have been introduced.
[0030] The coking pre-treatment for the molecular sieve, formed
with or without a binder, is carried out by introducing at least
one hydrocarbon molecule containing 4 to 20 carbon atoms, preferably
4 to 12 carbon atoms, preferably selected from the group formed
by monoolefins, polyolefins or alkanes, preferably alkanes containing
4 to 12 carbon atoms. The size of this molecule is such that it
can penetrate into the interior of the microporosity of the sieve.
[0031] Pre-treatment can also be effected by introducing the feed
to be converted if it contains the cited molecule(s). This pre-treatment
can thus advantageously be effected before the actual start of the
conversion reaction.
[0032] This is the case when linear olefins are isomerised.
[0033] Pre-treatment takes place prior to the isomerisation reaction,
i.e., on the sieve alone which is the catalyst, or on the sieve
alone before forming the catalyst, or on the catalyst containing
the sieve.
[0034] The process takes place at a space velocity in the range
0.1 h.sup.-1 to 45 h.sup.-1 preferably in the range 0.5 h.sup.-1
to 25 h.sup.-1 more preferably in the range 0.5 h.sup.-1 to 10
h.sup.-1 at a temperature in the range 300.degree. C. to 550.degree.
C., preferably in the range 400.degree. C. to 550.degree. C., and
advantageously more than 400.degree. C. to 535.degree. C., for a
period in the range 0.5 h to 48 h, preferably in the range 0.5 h
to 24 h, at a pressure of 0.1-1 MPa, more advantageously 0.1-0.5
MPa.
[0035] The feed used for pre-treatment, containing at least one
hydrocarbon molecule containing 4 to 20 carbon atoms, is advantageously
diluted, for example with an inert gas (nitrogen etc.). The process
is carried out in the absence of hydrogen.
[0036] After this treatment, the coke content in the molecular
sieve is such that the pore volume which is accessible to nitrogen
and measured by nitrogen adsorption is in the range 3% to 30% of
the pore volume of the uncoked starting sieve, preferably in the
range 5% to 20% and more preferably in the range 5% to 15% of the
pore volume of the non coked starting molecular sieve. This test
shows that coking occurs in the pores and not solely on the external
surface.
[0037] This pre-treatment leads to a considerable increase in the
selectivity of the catalyst, in particular for skeletal isomerisation
of olefins. This increase in selectivity originates from a very
marked reduction in the yield of products from the disproportionation
of the olefin in the feed and of paraffinic products which results
from a transfer of hydrogen from the coke precursors to the reactant.
Further, the activity of the molecular sieve is hardly changed by
the pre-treatment of the invention.
[0038] This process can produce improved performance, in particular
as regards sieve and/or catalyst stability.
[0039] The process described here is preferably carried out in
the reaction zone, in a reaction pre-zone or preferably in a dedicated
plant provided with the necessary equipment. It can also be carried
out in the reaction zone.
[0040] In the process for skeletal isomerisation of a feed containing
linear olefinic hydrocarbons containing 4 to 20 carbon atoms in
which the feed is brought into contact with a catalyst at a temperature
of 150-500.degree. C., a pressure of 0.01-1 MPa, a space velocity
of 0.1-10 h.sup.-1 the catalyst comprises a molecular sieve which
has been pre-treated in accordance with the process described above.
[0041] The feed to be isomerised is brought into contact with the
catalyst at a temperature in the range 150.degree. C. to 500.degree.
C., (preferably in the range 150.degree. C. to 450.degree. C., in
particular when the feed is constituted by butenes and/or pentenes),
at a pressure in the range 0.01 MPa to 1 MPa absolute (preferably
in the range 0.01 MPa to 0.5 MPa absolute in particular when the
feed is constituted by butenes and/or pentenes). The space velocity
is in the range 0.1 h.sup.-1 to 10 h.sup.-1 expressed as the volume
of olefinic feed per volume of catalyst per hour (preferably in
the range 0.5 h.sup.-1 to 6 h.sup.-1 in particular when the feed
is constituted by butenes and/or pentenes).
[0042] With the process of the invention, it is possible to isomerise
an olefinic C.sub.4 cut alone (after removing the C.sub.3 cut),
the whole of an olefinic C.sub.3-C.sub.4 cut, an olefinic C.sub.5
cut or more generally, linear olefinic hydrocarbons containing 4
to 20 carbon atoms per molecule, i.e., cuts containing mainly these
hydrocarbons.
[0043] The catalyst contains 5-100% of sieve, preferably 10-90%
by weight of sieve, advantageously 20-80%, the matrix preferably
being alumina.
[0044] The invention also concerns a catalyst containing at least
one molecular sieve selected from the group formed by SAPO-31 SAPO-11
Theta-1 EU-1 omega zeolite, mordenite, ferrierite, Nu-10 Nu-86
and Nu-87 said sieve having been subjected to the coking treatment
described above to render it selective.
[0045] The treatment is preferably carried out at a pressure of
0.1-0.5 MPa, between 400.degree. C. and 535.degree. C., in the absence
of hydrogen and using at least one olefin, polyolefin or an alkane
containing 4 to 12 carbon atoms.
[0046] The following examples illustrate the invention without
limiting its scope.
[0047] Isomerisation performance was expressed as follows:
[0048] Butene Conversion 1 C = S (% n-butenes)feed - S (% n-butenes)effluent
S (% n-butenes)feed .times. 100
[0049] Isobutene Selectivity 2 S = (% isobutene)effluent - (% isobutene)feed
S (% n-butenes)feed - S (% n-butenes)effluent .times. 100
[0050] Isobutene Yield
R=C.times.S/100
EXAMPLE 1
Catalyst 1 In Accordance With The Invention
[0051] 10 g of ferrierite, with a pore size of 0.42 nm.times.0.54
nm and 0.35 nm.times.0.48 nm, synthesised using the method described
in U.S. Pat. No. 4853203 and U.S. Pat. No. 4982046 in the acid
form and with a Si/Al atomic ratio of 13.8 was pelletized then
screened to obtain a fraction with a diameter which was in the range
0.2 mm to 0.5 mm, then 5 g of pelletized and sieved ferrierite was
introduced into a tube reactor for use as a fixed bed.
[0052] This ferrierite was then calcincd in dry air for 4 hours
at 550.degree. C. and then a coking pre-treatment was applied to
it. The pre-treatment consisted of introducing n-butenes (which
also constituted the feed to be isomerised) at a temperature of
500.degree. C. for 2 hours. The n-butenes were introduced diluted
in nitrogen at the following partial pressures: P.sub.n-butenes=0.2
bar and P.sub.N2=0.8 bar, at a space velocity of 2 grams of n-butenes
per gram of ferrierite per hour (2 h.sup.-1).
[0053] The reactor temperature was reduced to 350.degree. C., the
temperature of the n-butene isomerisation reaction, and the wwh
was held at 2 h.sup.-1.
[0054] The n-butene conversion, isobutene selectivities and isobutene
yields were measured after one hour of n-butene injection and are
shown in Table 1.
[0055] Similar results were obtained with a catalyst constituted
by 80% by weight of the zeolite used in this example and 20% by
weight of alumina.
EXAMPLE 2
Catalyst 2 Not In Accordance With The Invention
[0056] The same ferrierite as that used for Example 1 was used
in the same procedure in a fixed bed reactor and calcined at 550.degree.
C. for 4 hours
[0057] It then underwent pre-treatment which consisted of introducing
n-butenes to be isomerised at a temperature of 120.degree. C. for
2 hours. The n-butenes were introduced diluted in nitrogen at the
following partial pressures: P.sub.n-butenes=0.2 bar and P.sub.N2=0.8
bar, at a space velocity of 2 grams of n-butenes per gram of ferrierite
per hour (2 h.sup.-1).
[0058] The reactor temperature was raised to 350.degree. C., the
temperature of the n-butene isomerisation reaction, and the wwh
was held at 2 h.sup.-1.
[0059] The n-butene conversion, isobutene selectivities and isobutene
yields were measured after one hour of n-butene injection and are
shown in Table 1.
1 TABLE 1 n-butene Isobutene conversion selectivity Isobutene yield
(weight %) (weight %) (weight %) Example 1 in 45 90 40.5 accordance
with invention Example 2 not in 50 60 30 accordance with invention
[0060] The table shows the influence of pretreating the ferrierite
in accordance with the invention on the isobutene selectivities
and yields which in this case were higher than when no pre-treatment
in accordance with the invention was applied.
EXAMPLE 3
Catalyst 3 In Accordance With The Invention
[0061] 10 g of ZSM-23 zeolite of structure type MTT, synthesised
using the method described in European patent EP-A-0 347 273 in
its acid form and with a Si/Al atomic ratio of 50 was pelletized,
then screened to obtain a fraction with a diameter in the range
0.2 mm to 0.5 mm, then 5 g of pelletized and screened ZSM-23 was
introduced into a tube reactor for use as a fixed bed.
[0062] This ZSM-23 zeolite was then calcined in dry air for 4 hours
at 550.degree. C. and then a coking pre-treatment was applied to
it. The pre-treatment consisted of introducing n-butenes to be isomerised
at a temperature of 500.degree. C. for 2 hours. The n-butenes were
introduced diluted in nitrogen at the following partial pressures:
P.sub.n-butenes=0.2 bar and P.sub.N2=0.8 bar, at a space velocity
of 2 grams of n-butenes per gram of ZSM-23 per hour (2 h.sup.-1).
[0063] The reactor temperature was reduced to 350.degree. C., the
temperature of the n-butene isomerisation reaction, and the wwh
was held at 2 h.sup.-1.
[0064] The n-butene conversion, isobutene selectivities and isobutene
yields were measured after one hour of n-butene injection and are
shown in Table 2.
[0065] Similar results were obtained with a catalyst constituted
by 80% by weight of the zeolite used in this example and 20% by
weight of alumina.
EXAMPLE 4
Catalyst 4 Not In Accordance With The Invention
[0066] The same ZSM-23 zeolite as that used in Example 3 was used
in the same procedure in a fixed bed reactor, and calcined at 550.degree.
C. for 4 hours.
[0067] It then underwent pre-treatment which consisted of introducing
n-butenes to be isomerised at a temperature of 150.degree. C. for
2 hours. The n-butenes were introduced diluted in nitrogen at the
following partial pressures: P.sub.n-butenes=0.2 bar and P.sub.N2=0.8
bar, at a space velocity of 2 grams of n-butenes per gram of ZSM-23
per hour (2 h.sup.-1).
[0068] The reactor temperature was then raised to 350.degree. C.,
the temperature of the n-butene isomerisation reaction, and the
wwh was held at 2 h.sup.-1.
[0069] The n-butene conversion, isobutene selectivities and isobutene
yields were measured after one hour of n-butene injection and are
shown in Table 2.
2 TABLE 2 n-butene Isobutene conversion selectivity Isobutene yield
(weight %) (weight %) (weight %) Example 3 in 46 40 18.4 accordance
with invention Example 4 not in 52 20 10.4 accordance with invention
[0070] The table shows the influence of a pretreating the ZSM-23
in accordance with the invention on the isobutene selectivities
and yields which in this case were higher than when no pre-treatment
in accordance with the invention was applied.
[0071] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating condition of this invention for those used in the
preceding examples.
[0072] The entire disclosure of all application, patents and publications,
cited above and below, and of corresponding French application 95/05463
are hereby incorporated by reference.
[0073] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention,
and without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions. |