Molecular sieve abstract
A process for oligomerizing olefins in the liquid phase using nickel-containing
silicaceous crystalline molecular sieve catalyst.
Molecular sieve claims
What is claimed is:
1. A process for oligomerizing alkenes comprising:
(a) contacting a C.sub.2 to C.sub.20 olefin or mixture thereof
in the liquid phase with a nickel-containing silicaceous crystalline
molecular sieve in the hydrogen form selected from the group consisting
of silicalite, an organosilicate disclosed in U.S. Pat. No. RE 29948
and CZM or mixtures thereof, at a temperature from about 45.degree.
F. to about 450.degree. F.;
(b) recovering an effluent comprising oligomerized alkene.
2. The process of claim 1 wherein the nickel-containing silicaceous
crystalline molecular sieve also contains zinc cation.
3. The process of claim 1 wherein said contacting is carried out
at a LHSV of from about 0.2 to 5.
4. The process of claim 1 wherein the pressure is from about 50
to about 1600 psig.
5. The process of claim 1 wherein said nickel-containing silicaceous
crystalline molecular sieve is silicalite.
6. The process of claim 1 wherein said nickel-containing silicaceous
crystalline molecular sieve is organosilicate disclosed in U.S.
Pat. No. RE 29948.
7. The process of claim 1 wherein said nickel-containing silicaceous
crystalline molecular sieve is CZM.
8. The process of claim 5 wherein the nickel-containing silicaceous
crystalline molecular sieve also contains zinc cation.
9. The process of claim 6 wherein the nickel-containing silicaceous
crystalline molecular sieve also contains zinc cation.
10. The process of claim 7 wherein said nickel-containing silicaceous
crystalline molecular sieve also contains zinc cation.
11. The process of claim 1 wherein said alkenes comprise n-alkenes.
12. The process of claim 15 wherein said n-alkenes are l-alkenes.
13. The process of claim 1 wherein said alkenes comprise branched
chain alkenes and wherein the branches of said branched chain alkenes
are methyl branches.
14. The process of claim 1 further comprising the step of hydrogenating
said alkene oligomers.
15. The process of claim 1 further comprising the steps of: separating
unreacted alkenes present in said effluent from alkene oligomers
present in said effluent and recycling said unreacted alkenes into
the feed for said contacting step.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention is in the field of olefin oligomerization.
More specifically, the present invention relates to oligomerization
of olefins in the liquid phase with a nickel-containing silicaceous
crystalline molecular sieve catalyst.
2. Description of the Prior Art
Oligomerization and polymerization of olefins in the gas phase
over various zeolites is known in the art. For example, U.S. Pat.
No. 3960978 a process for producing a gasoline fraction containing
predominantly olefinic compounds which comprises contacting a C.sub.2
to C.sub.5 olefin with a ZSM-5 type crystalline aluminosilicate
zeolite at a temperature of from about 500.degree. F. to about 900.degree.
F. as disclosed.
U.S. Pat. No. 4021501 describes the conversion of gaseous C.sub.2
to C.sub.5 olefins into gasoline blending stock by passage over
ZSM-12 at temperatures of from about 400.degree. F. to about 1200.degree.
F.
U.S. Pat. No. 4211640 discloses a process for the treatment of
highly olefinic gasoline containing at least about 50% by weight
of olefins by contacting said olefinic gasoline with crystalline
aluminosilicate zeolites, such as those of the ZSM-5 type, so as
to selectively react olefins other than ethylene and produce both
gasoline and fuel oil.
U.S. Pat. No. 4254295 discloses a process for the oligomerization
of olefins by contacting said olefins in the liquid phase with ZSM-12
catalyst at temperatures of 80.degree. F. to 400.degree. F.
U.S. Pat. No. 4227992 discloses a process for separating ethylene
in admixture with light olefins by contacting said olefinic mixture
with a ZSM-5 catalyst and thus producing both gasoline and fuel
oil range materials.
The processes disclosed in these patents differ from that of the
present invention in that they employ either a different catalyst,
higher temperatures, or reaction in the gaseous phase.
Also, an important feature of several of the catalysts used in
these prior art processes is that the catalyst must have reduced
activity before oligomerization. Such catalyst of reduced activity
may be obtained by steaming or by use in a previous conversion process.
This deactivation step is not required in the process of the present
invention.
SUMMARY OF THE INVENTION
In accordance with the present invention, there has been discovered
a process for oligomerizing alkenes comprising: (a) contacting a
C.sub.2 to C.sub.20 olefin or mixture thereof in the liquid phase
with a nickel-containing silicaceous crystalline molecular sieve
in the hydrogen form selected from the group consisting of silicalite,
an organosilicate disclosed in U.S. Pat. No. RE 29948 CZM or mixtures
thereof, at a temperature from about 45.degree. F. to about 450.degree.
F.; (b) recovering an effluent comprising oligomerized alkene.
It has been found that the present process provides selective conversion
of the olefin feed to oligomer products. The present process effects
the conversion of the olefin feed to dimer, trimer, tetramer, etc.,
products with high selectivity. The product of the present reaction
thus contains primarily olefin oligomer and little or no light cracked
products, paraffins, etc.
The high selectivity is in part due to the surprisingly high oligomerization
activity of the catalyst of the present process, which permits high
conversion at low temperatures where cracking reactions are minimized.
The oligomers which are the products of the process of this invention
are medium to heavy olefins which are highly useful for both fuels
and chemicals. These include olefinic gasoline, such as from propylene
dimerization, and extremely high quality midbarrel fuels, such as
jet fuel. Higher molecular weight compounds can be used without
further reaction as components of functional fluids such as lubricants,
as viscosity index improvers in lubricants, as hydraulic fluids,
as transmission fluids, and as insulating oils, e.g., in transformers
to replace PCB containing oils. These olefins can also undergo chemical
reactions to produce surfactants which in turn can be used as additives
to improve the operating characteristics of the compositions to
which they are added (e.g., lubricating oils) or can be used as
primary surfactants in highly important activities such as enhanced
oil recovery or as detergents. Among the most used surfactants prepared
from the heavy olefins are alkyl sulfonates and alkyl aryl sulfonates.
A significant feature of the present process is the liquid phase
contacting of the olefin feed and the nickel-containing silicaceous
crystalline molecular sieves. There will be appreciated that the
pressures and temperatures employed must be sufficient to maintain
the system in the liquid phase. As is known to those in the art,
the pressure will be a function of the number of carbon atoms of
the feed olefin and the temperature.
The oligomerization process described herein may be carried out
as a batch type, semi-continuous or continuous operation utilizing
a fixed or moving bed catalyst system.
DESCRIPTION OF SPECIFIC EMBODIMENTS
The feeds used in the process of the invention contain alkenes
which are liquids under the conditions in the oligomerization reaction
zone. Under standard operating procedures it is normal both to know
the chemical composition of feedstocks being introduced into a reaction
zone and to set and control the temperature and pressure in the
reaction zone. Once the chemical composition of a feedstock is known,
the temperature and hydrocarbon partial pressures which will maintain
all or part of the feed as liquids can be determined using standard
tables or routine calculations. Conversely, once the desired temperature
and pressure to be used in the reaction zone are set, it becomes
a matter of routine to determine what feeds and feed components
would or would not be liquids in the reactor. These calculations
involve using critical temperatures and pressures. Critical temperatures
and pressures for pure organic compounds can be found in standard
reference works such as CRC Handbook of Chemistry and Physics, International
Critical Tables, Handbook of Tables for Applied Engineering Science,
and Kudchaker, Alani, and Zwolinski, Chemical Reviews 68 659 (1968),
all of which are incorporated herein by reference. The critical
temperature for a pure compound is that temperature above which
the compound cannot be liquefied regardless of pressure. The critical
pressure is the vapor pressure of the pure compound at its critical
temperature. These points for several pure alkenes are listed below:
It can be appreciated that at temperatures above about 205.degree.
C. (401.degree. F.), pure C.sub.5 and lower alkenes must be gaseous,
while pure C.sub.6 and higher alkenes can still be liquefied by
applying pressure. Similarly, above about 275.degree. C. (527.degree.
F.) pure C.sub.8 and higher alkenes can be maintained in the liquid
state, while pure C.sub.7 and lower alkenes must be gaseous.
Typical feeds are mixtures of compounds. But even so, once the
chemical composition of the feed is known, the critical temperature
and pressure of the mixture can be determined from the ratios of
the chemicals and the critical points of the pure compounds. See
for example, the methods of Kay and Edmister in Perry's Chemical
Engineers Handbook, 4th Edition, pages 3-214 3-215 (McGraw Hill,
1963), which is incorporated by reference.
Of course, the only constraint on the alkenes present in the feed
and which are to react in the oligomerization reaction zone is that
these alkenes be liquids under the conditions in the reaction zone
(the conditions include a temperature of less than about 450.degree.
F.). The chemical composition of the alkenes can be varied to obtain
any desired reaction mixture or produce mix, so long as at least
some of the alkene components of the feed are liquid.
The alkene chains can be branched. And, even though the nickel-containing
silicaceous crystalline molecular sieve catalysts used in this invention
are intermediate pore size molecular sieves, alkenes having quaternary
carbons (two branches on the same carbon atom) can be used. But
where quaternary carbons are present, it is preferred that the branches
are methyl.
The preferred alkenes are straight chain, or n-alkenes, and the
preferred n-alkenes are l-alkenes. The alkenes have from 2 to 20
carbon atoms, and more preferably have from about 2 to about 6 carbon
atoms.
One of the surprising discoveries of this invention is that under
certain reaction conditions, longer chain alkenes can be polymerized
instead of being cracked to short chain compounds. Additionally,
the oligomers produced from long n-l-alkenes are very highly desirable
for use as lubricants. The oligomers have surprisingly little branching
so they have very high viscosity indices, yet they have enough branching
to have very low pour points.
The feed alkenes can be prepared from any source by standard methods.
Sources of such olefins can include FCC offgas, coker offgas, syngas
(by use of CO reduction catalysts), low pressure, nonhydrogenative
zeolite dewaxing, alkanols (using high silica zeolites), and dewaxing
with crystalline silica polymorphs. Highly suitable n-l-alkene feeds,
especially for preparing lubricating oil basestocks, can be obtained
by thermal cracking of hydrocarbonaceous compositions which contain
normal paraffins or by Ziegler polymerization of ethene.
Often, suitable feeds are prepared from lower alkenes which themselves
are polymerized. Such feeds including polymer gasoline from bulk
H.sub.3 PO.sub.4 polymerization, and propylene dimer, and other
olefinic polymers in the C.sub.4 -C.sub.20 range prepared by processes
known to the art.
The nickel-containing silicaceous crystalline molecular sieves
used in this invention are of intermediate pore size. By "intermediate
pore size", as used herein, is meant an effective pore aperture
in the range of about 5 to 6.5 Angstroms when the molecular sieve
is in the H-form. Molecular sieves having pore apertures in this
range tend to have unique molecular sieving characteristics. Unlike
small pore zeolites such as erionite and chabazite, they will allow
hydrocarbons having some branching into the molecular sieve void
spaces. Unlike larger pore zeolites such as faujasites and mordenites,
they can differentiate between n-alkanes and slightly branched alkanes
on the one hand and larger branched alkanes having, for example,
quaternary carbon atoms.
The effective pore size of the molecular sieves can be measured
using standard adsorption techniques and hydrocarbonaceous compounds
of known minimum kinetic diameters. See Breck, Zeolite Molecular
Sieves, 1974 (especially Chapter 8) and Anderson et al, J. Catalysis
58 114 (1979), both of which are incorporated by reference.
Intermediate pore size molecular sieves in the H-form will typically
admit molecules having kinetic diameters of 5.0 to 6.5 Angstroms
with little hindrance. Examples of such compounds (and their kinetic
diameters in Angstroms) are: n-hexane (4.3), 3-methylpentane (5.5),
benzene (5.8). Compound having kinetic diameters of about 6 to 6.5
Angstroms can be admitted into the pores, depending on the particular
sieve, but do not penetrate as quickly and in some cases are effectively
excluded. Compounds having kinetic diameters in the range of 6 to
6.5 Angstroms include: cyclohexane (6.0), 23-dimethylbutane (6.1),
m-xylene (6.1), and 1234-tetramethylbenzene (6.4). Generally,
compounds having kinetic diameters of greater than about 6.5 Angstroms
do not penetrate the pore apertures and thus are not absorbed into
the interior of the molecular sieve lattice. Examples of such larger
compounds include: o-xylene (6.8), hexamethylbenzene (7.1), 135-trimethylbenzene
(7.5), and tributylamine (8.1).
The preferred effective pore size range is from about 5.3 to about
6.2 Angstroms.
In performing adsorption measurements to determine pore size, standard
techniques are used. It is convenient to consider a particular molecule
as excluded if it does not reach at least 95% of its equilibrium
adsorption value on the zeolite in less than about 10 minutes (p/po=0.5;
25.degree. C.).
Silicalite is disclosed in U.S. Pat. No. 4061724; the "RE
29948 organosilicates" are disclosed in U.S. Pat. No. RE 29948;
chromia silicates, CZM, are disclosed in Ser. No. 450419 Miller,
filed Dec. 16 1982. These patents are incorporated herein by reference.
The crystalline silica polymorphs, silicalite, and U.S. Pat. No.
RE 29948 organosilicates, and the chromia silicate, CZM are essentially
alumina free.
"Essentially alumina free", as used herein, is meant
the product silica polymorph (or essentially alumina-free silicaceous
crystalline molecular sieve) has a silica:alumina mole ratio of
greater than 200:1 preferably greater than 500:1. The term "essentially
alumina free" is used because it is difficult to prepare completely
aluminum free reaction mixtures for synthesizing these materials.
Especially when commercial silica sources are used, aluminum is
almost always present to a greater or lesser degree. The hydrothermal
reaction mixtures from which the essentially alumina free crystalline
silicaceous molecular sieves are prepared can also be referred to
as being substantially aluminum free. By this usage is meant that
no aluminum is intentionally added to the reaction mixture, e.g.,
as an alumina or aluminate reagent, and that to the extent aluminum
is present, it occurs only as a contaminant in the reagents.
The most preferred molecular sieve is the zeolite Ni-silicalite.
Of course, these and the other molecular sieves can be used in physical
admixtures.
When synthesized in the alkali metal form, the zeolites may be
conveniently converted to the hydrogen form by well known ion exchange
reactions, for example, by intermediate formation of the ammonium
form as a result of ammonium ion exchange and calcination of the
ammonium form to yield the hydrogen form or by treatment with dilute
acid such as hydrochloric acid.
Nickel is incorporated into these silicaceous crystalline molecular
sieves according to techniques well known in the art such as impregnation
and cation exchange. For example, typical ion exchange techniques
would be to contact the particular sieve in the hydrogen form with
an aqueous solution of a nickel salt. Although a wide variety of
salts can be employed, a particular preference is given to chlorides,
nitrates and sulfates. The amount of nickel in the zeolites range
from 0.5% to 10% by weight and preferably from 1% to 5% by weight.
Representative ion exchange techniques are disclosed in a wide
variety of patents including U.S. Pat. Nos. 3140249; 3140251;
3960978 3140253 and 4061724.
Following contact with the salt solution, the zeolites are preferably
washed with water and dried at a temperature ranging from 150.degree.
F. to about 500.degree. F. and thereafter heated in air at temperatures
ranging from about 500.degree. F. to 1000.degree. F. for periods
of time ranging from 1 to 48 hours or more.
The nickel-containing silicaceous crystalline molecular sieve catalysts
can be made substantially more stable for oligomerization by including
from about 0.2% to 3% by weight and preferably 0.5% to 2% by weight
of the Group IIB metals, zinc or cadmium and preferaby zinc. A primary
characteristic of these substituents is that they are weak bases,
and are not easily reduced. These metals can be incorporated into
the catalysts using standard impregnation, ion exchange, etc., techniques.
Strongly basic metals such as the alkali metals are unsatisfactory
as they poison substantially all of the polymerization sites on
the zeolite. For this reason, the alkali metal content of the zeolite
is less than 1%, preferably less than 0.1%, and most preferably
less than 0.01%. The feed should be low in water, i.e., less than
100 ppm, more preferably less than 10 ppm, in sulfur, i.e., less
than 100 ppm and preferably less than 10 ppm, in diolefins, i.e.,
less than 0.5%, preferably less than 0.05% and most preferably less
than 0.01%, and especially in nitrogen, i.e., less than 5 ppm, preferably
less than 1 ppm and most preferably less than 0.2 ppm.
The polymerization processes of the present invention are surprisingly
more efficient with small crystallite sieve particles than with
larger crystalline particles. Preferably, the molecular sieve crystals
or crystallites are less than about 10 microns, more preferably
less than about 1 micron, and most preferably less than about 0.1
micron in the largest dimension. Methods for making molecular sieve
crystals in different physical size ranges are known to the art.
The molecular sieves can be composited with inorganic matrix materials,
or they can be used with an organic binder. It is preferred to use
an inorganic matrix since the molecular sieves, because of their
large internal pore volumes, tend to be fragile, and to be subject
to physical collapse and attrition during normal loading and unloading
of the reaction zones as well as during the oligomerization processes.
Where an inorganic matrix is used, it is highly preferred that the
matrix be substantially free of hydrocarbon conversion activity.
It can be appreciated that if an inorganic matrix having hydrogen
transfer activity is used, a significant portion of the oligomers
which are produced by the molecular sieve may be converted to paraffins
and aromatics and to a large degree the benefits of my invention
will be lost.
The reaction conditions under which the oligomerization reactions
take place include hydrocarbon partial pressures sufficient to maintain
the desired alkene reactants in the liquid state in the reaction
zone. Of course, the larger the alkene molecules, the lower the
pressure required to maintain the liquid state at a given temperature.
As described above, the operating pressure is intimately related
to the chemical composition of the feed, but can be readily determined.
Thus, the required hydrocarbon partial pressure can range from 31
bar at 450.degree. F. for a pure n-l-hexene feed to about atmospheric
pressure for a n-l-C.sub.15 -C.sub.20 alkene mixture. In the process
of this invention, both reactant and product are liquids under the
conditions in the reaction zone, thus leading to a relatively high
residence time of each molecule in the catalyst.
The reaction zone is typically operated below about 450.degree.
F. Above that temperature not only significant cracking of reactants
and loss of oligomer product take place, but also significant hydrogen
transfer reactions causing loss of olefinic oligomers to paraffins
and aromatics take place. An oligomerization temperature in the
range from about 90.degree. F. to 350.degree. F. is preferred. Liquid
hourly space velocities can range from 0.05 to 20 preferably from
0.1 to about 4.
Once the effluent from the oligomerization reaction zone is recovered,
a number of further processing steps can be performed.
If it is desired to use the long chain compounds which have been
formed in middle distillate fuel such as jet of diesel or in the
lube oils as base stock, the alkene oligomers are preferably hydrogenated.
All or part of the effluent can be contacted with the molecular
sieve catalyst in further reaction zones to further react unreacted
alkenes and alkene oligomers with themselves and each other to form
still longer chain materials. Of course, the longer the carbon chain,
the more susceptible the compound is to being cracked. Therefore,
where successive oligomerization zones are used, the conditions
in each zone must not be so severe as to crack the oligomers. Operating
with oligomerization zones in series can also make process control
of the exothermic oligomerization reactions much easier.
One particularly desirable method of operation is to separate unreacted
alkenes present in the effluent from the alkene oligomers present
in the effluent and then to recycle the unreacted alkenes back into
the feed.
The following examples further illustrate this invention.
EXAMPLES
Example 1
A Zn-silicalite catalyst was prepared in the following manner.
H-silicalite of 240 SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio was mixed
with peptized and neutralized Catapal alumina at a 67/33 sieve/alumina
weight ratio, extruded through a 1/16" die, dried overnight
at 300.degree. F. under N.sub.2 then calcined in air for 8 hours
at 850.degree. F. The catalyst was impregnated by the pore-fill
method to 1 weight % Zn using an aqueous solution of Zn(NO.sub.3).sub.2
then dried and calcined as done previously.
Example 2
The catalyst of Example 1 was impregnated to 3 weight % Ni by the
pore-fill method using an aqueous solution of Ni(NO.sub.3).sub.2.6H.sub.2
O. The catalyst was dried overnight under N.sub.2 at 300.degree.
F., then calcined in air for 8 hours at 850.degree. F.
Example 3
The Zn-silicalite catalyst of Example 1 was tested for converting
propylene to higher molecular weight products at 150.degree. F.,
1000 psig, and 0.5 LHSV. At 24 hours onstream, conversion to C.sub.5
+ was 3.2% with 38% selectivity to dimer.
Example 4
The Ni-Zn-silicalite catalyst of Example 2 was tested for converting
propylene at the same conditions as in Example 3. At 40 hours onstream,
conversion to C.sub.5 + was 72.7% with 77% selectivity to dimer. |