Molecular sieve abstract
The invention concerns a process for skeletal isomerization 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.degree.-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
We claim:
1. A process for skeletal isomerization of an olefinic feed containing
linear olefinic hydrocarbons containing 4 to 20 carbon atoms using
a catalyst containing at least one molecular sieve with a pore size
of 0.4 nm to 0.8 nm, said process comprising, prior to commencing
the process, contacting said sieve with a pretreatment feed containing
at least one hydrocarbon of 4 to 20 carbon atoms, said pretreatment
feed being diluted in a inert gas, at a space velocity of 0.1-45
h.sup.-1 a temperature of 300.degree.-550.degree. C., and at a
pressure of 0.1-1 MPa for 0.5-48 h, whereby coke is deposited in
said pores in said sieve, and then contacting said olefinic feed
with the catalyst under skeletal isomerization conditions.
2. A process according to claim 1 wherein the hydrocarbon in said
pretreatment feed contains 4 to 12 carbon atoms.
3. A process according to claim 1 wherein the hydrocarbon in said
pretreatment feed is a monoolefin, polyolefin or an alkane.
4. A process according to claim 1 wherein the hydrocarbon in said
pretreatment feed is diluted in nitrogen.
5. A process according to claim 1 wherein the skeletal isomerization
temperature is 400.degree. C. to 535.degree. C., the pressure is
0.1 MPa to 9.5 MPa, the space velocity is 0.5 h.sup.-1 to 25 h.sup.-1
and the duration is 0.5 h to 24 h.
6. A process according to claim 1 wherein the molecular sieve has
a pore size 0.4 nm to 0.7 nm.
7. A process according to claim 1 wherein the molecular sieve includes
a one-dimensional microporous network.
8. A process according to claim 1 wherein the molecular sieve is
ferrierite, SAPO-31 SAPO-11 Theta-1 EU-1 ZSM-12 ZSM-23 omega
zeolite, mordenite, Nu-10 Nu-86 or Nu-87.
9. A process according to claim 1 wherein the catalyst further
contains a matrix and wherein the molecular sieve is contacted with
the pretreatment feed before combination with the matrix.
10. A process according to claim 1 wherein the molecular sieve
is contacted with the pretreatment feed after combination with the
matrix.
11. A process according to claim 1 wherein the sieve is contacted
with the pretreatment feed outside the reaction zone.
12. A process according to claim 2 in which the skeletal isomerization
conditions comprise a temperature of 150.degree.-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 claim 1 wherein the olefinic feed is
an olefinic C.sub.4 feed.
14. A process according to claim 1 wherein the olefinic feed is
an olefinic C.sub.5 feed.
15. A process for skeletal isomerisation of a feed containing linear
olefinic hydrocarbons containing 4 to 20 carbon atoms, comprising
contacting said feed with a catalyst prepared by a process wherein
a zeolitic molecular sieve with a pore size of 0.4 nm to 0.8 nm
is contacted with a feed containing at least one hydrocarbon of
4 to 20 carbon atoms, diluted in an inert gas, at a space velocity
of 0.1-45 h.sup.-1 a temperature of 300.degree.-550.degree. C.,
and at a pressure of 0.1-1 MPa for 0.5-48 h. whereby coke is deposited
in said pores in said sieve.
16. A process for skeletal isomerisation of a feed containing linear
olefinic hydrocarbons containing 4 to 20 carbon atoms, comprising
contacting said feed under isomerization conditions with a catalyst
prepared by a process wherein a zeolitic molecular sieve selected
from the group consisting of ferrierite, Theta-1 EU-1 omega zeolite,
mordenite, Nu-10 Nu-86 and Nu-87 is contacted with a feed containing
at least one hydrocarbon of 4 to 20 carbon atoms, diluted in an
inert gas, at a space velocity of 0.1-45 h.sup.-1 a temperature
of 300.degree.-550.degree. C., and at a pressure of 0.1-1 MPa for
0.5-48 h, whereby coke is deposited in said pores in said sieve.
17. A process for skeletal isomerization of an olefinic feed containing
linear olefinic hydrocarbons containing 4 to 20 carbon atoms using
a catalyst containing at least one zeolitic molecular sieve with
a pore size of 0.4 nm to 0.8 nm, said process comprising, prior
to commencing the process, contacting said sieve with a pretreatment
feed containing at least one hydrocarbon of 4 to 20 carbon atoms,
at a space velocity of 0.1-45 h.sup.-1 a temperature of 300.degree.-550.degree.
C., and at a pressure of 0.1-1 MPa for 0.5-48 h, whereby coke is
deposited in said pores in said sieve, and then contacting said
olefinic feed with the catalyst under isomerization conditions.
18. A process according to claim 17 wherein said pretreatment
feed is diluted in an inert gas.
19. A process according to claim 1 wherein the molecular sieve
is ferrierite, Theta-1 EU-1 ZSM-12 ZSM-23 omega zeolite, mordenite,
Nu-10 Nu-86 or Nu-87.
Molecular sieve description
The invention concerns a process for skeletal isomerization 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.
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.
BACKGROUND OF THE INVENTION
Processes for treatment by coking have already been described for
catalysts used for aromatic alkylation or isomerization, or for
the oligomerisation of olefins.
U.S. Pat. No. 4508836 describes a treatment process applied to
a catalyst used to convert aromatic feeds by alkylation or isomerization,
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 involves 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., deposit more than 1% of
coke.
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.degree.-500.degree. C. and
at a pressure of more than 27 bars.
In the present invention, oligomerisation of the olefins (i.e.,
polymerisation), which would reduce the yield, must be avoided.
Because of the reduction in the level of lead alkyls in fuel over
the past few years, the refiner has had to plan to incorporate different
compounds into the fuel, 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 fuel quality and increase the
octane number by a greater amount than that obtained with methanol.
MTBE has other advantages, such as:
a boiling point which corresponds to that of the petrol components
with the poorest antiknock properties;
a vapor pressure which is compatible with those components;
an excellent freezing point;
low solubility in water;
complete miscibility with hydrocarbons, etc.
MTBE is generally obtained from isobutene and methanol in the following
reaction: ##STR1##
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.
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
isomerized.
A number of processes associated with a number of catalysts have
been proposed in the literature.
Those catalysts are generally based on alumina or on molecular
sieves.
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:
deactivation due to the formation of a large quantity of coke;
formation of unwanted products such as dimers and trimers of butenes
and aromatic compounds.
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.
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 523838 EP 501577) can constitute the active phases in catalysts
for the skeletal isomerization of linear olefins.
The structures cited in the above patents are ferrierite, SAPO-11
and a mordenite which has been exchanged with magnesium.
SUMMARY OF THE IVENTION
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 isomerization of olefins
(for example n-butenes). These catalysts also have good catalytic
stabilities.
One object of the invention is to provide a skeletal isomerization
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.degree.-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.
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 5 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.
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.
The sieve can also be used as it is, without a matrix.
Elements from various groups in the periodic classification may
optionally have been introduced.
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.
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.
This is the case when linear olefins are isomerized.
Pre-treatment takes place prior to the isomerization 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.
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.
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.
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.
This pre-treatment leads to a considerable increase in the selectivity
of the catalyst, in particular for skeletal isomerization 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.
This process can produce improved performance, in particular as
regards sieve and/or catalyst stability.
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.
In the process for skeletal isomerization 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.degree.-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.
The feed to be isomerized 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).
With the process of the invention, it is possible to isomerize
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.
The catalyst contains 5-100% of sieve, preferably 10-90% by weight
of sieve, advantageously 20-80%, the matrix preferably being alumina.
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.
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. |