Olefin oligomerization with surface modified zeolite

A process for producing substantially linear hydrocarbons by oligomerizing a lower olefin at elevated temperature and pressure which comprises contacting the lower olefin under oligomerization/polymerization conditions with siliceous acidic ZSM-23 zeolite having Bronsted acid activity; wherein the zeolite has acidic pore activity and wherein the zeolite surface is rendered substantially inactive for acidic reactions. The zeolite surface can be neutralized by a bulky pyridine compound having an effective cross-section larger than the zeolite pore. The preferred deactivating agent is 2,4,6-collidine, which may be applied to the zeolite as a pretreatment or added with olefin feed in a continuous process.

FIELD OF THE INVENTION 
The invention relates to a process for producing high molecular weight 
hydrocarbons from a lower olefin feedstock by employing a shape selective 
crystalline silicate catalyst which is surface inactivated. 
BACKGROUND OF THE INVENTION 
Recent work in the field of olefin upgrading has resulted in a catalytic 
process for converting lower olefins to heavier hydrocarbons. Heavy 
distillate and lubricant range hydrocarbons can be synthesized over ZSM-5 
type catalysts at elevated temperature and pressure to provide a product 
having substantially linear molecular conformations due to the ellipsoidal 
shape selectivity of certain medium pore catalysts. 
Conversion of olefins to gasoline and/or distillate products is disclosed 
in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens, Plank and Rosinski) 
wherein gaseous olefins in the range of ethylene to pentene, either alone 
or in admixture with paraffins are converted into an olefinic gasoline 
blending stock by contacting the olefins with a catalyst bed made up of a 
ZSM-5 type zeolite. Particular interest is shown in a technique developed 
by Garwood, et al., as disclosed in European Patent Application No. 
83301391.5, published Sept. 29, 1983. In U.S. Pat. Nos. 4,150,062; 
4,211,640; 4,227,992; and 4,547,613 Garwood, et al. disclose the operating 
conditions for the Mobil Olefin to Gasoline/Distillate (MOGD) process for 
selective conversion of C.sub.3.sup.+ olefins to mainly aliphatic 
hydrocarbons. 
In the process for catalytic conversion of olefins to heavier hydrocarbons 
by catalytic oligomerization using a medium pore shape selective acid 
crystalline zeolite, process conditions can be varied to favor the 
formation of hydrocarbons of varying molecular weight. At moderate 
temperature and relatively high pressure, the conversion conditions favor 
C.sub.10.sup.+ aliphatic product. Lower olefinic feedstocks containing 
C.sub.2 -C.sub.8 alkenes may be converted; however, the distillate mode 
conditions do not convert a major fraction of ethylene. A typical reactive 
feedstock consists essentially of C.sub.3 -C.sub.6 mono-olefins, with 
varying amounts of non-reactive paraffins and the like being acceptable 
components. 
Although it is known to use basic materials to deactivate the Bronsted acid 
sites on the surface of aluminosilicate catalysts (see U.S. Pat. No. 
4,520,221 and U.S. Pat. No. 4,568,786, Chen, et al., incorporated herein 
by reference), the basic materials employed are bulky amines, such as 
di-tert-butyl pyridine. 
Shape-selective oligomerization, as it applies to the conversion of C.sub.2 
-C.sub.10 olefins over ZSM-5, is known to produce higher olefins up to 
C.sub.30 and higher. As reported by Garwood in "Intrazeolite Chemistry 
23", (Amer. Chem. Soc., 1983), reaction conditions favoring higher 
molecular weight product are low temperature (200.degree.-260.degree. C.), 
elevated pressure (about 2000 kPa or greater), and long contact time (less 
than 1 WHSV). The reaction under these conditions proceeds through the 
acid-catalyzed steps of (1) oligomerization, (2) isomerization-cracking to 
a mixture of intermediate carbon number olefins, and (3) 
interpolymerization to give a continuous boiling product containing all 
carbon numbers. The channel systems of medium pore catalysts impose 
shape-selective constraints on the configuration of the large molecules, 
accounting for the differences with other catalysts. 
The desired oligomerization-polymerization products include C.sub.10.sup.+ 
substantially linear aliphatic hydrocarbons. This catalytic path for 
propylene feed provides a long chain which may have one or more lower 
alkyl (e.g., methyl) substituents along the straight chain. 
The final molecular configuration is influenced by the pore structure of 
the catalyst. For the higher carbon numbers, the structure is primarily a 
methyl-branched straight olefinic chain, with the maximum cross-section of 
the chain limited by the dimension of the largest zeolite pore. Although 
emphasis is placed on the normal 1-alkenes as feedstocks, other lower 
olefins, such as 2-butene or isobutylene, are readily employed as starting 
materials due to rapid isomerization over the acidic zeolite catalysts. At 
conditions chosen to maximize heavy distillate and lubricant range 
products (C.sub.20.sup.+), the raw aliphatic product is essentially 
mono-olefinic. Overall branching is not extensive and may occur at spaced 
positions within the molecule. 
The viscosity index of a hydrocarbon lube oil is related to its molecular 
configuration. Extensive branching in a molecule usually results in a low 
viscosity index. It is believed that two modes of 
oligomerization/polymerization of olefins can take place over acidic 
zeolites, such as HZSM-5. One reaction sequence takes place at Bronsted 
acid sites inside the channels or pores, producing essentially linear 
materials. The other reaction sequence occurs on the outer surface, 
producing more branched material. By decreasing the surface acid activity 
of such zeolites, fewer highly branched products with low VI are obtained. 
Several techniques may be used to increase the relative ratio of 
intra-crystalline acid sites to surface active sites. This ratio increases 
with crystal size due to geometric relationship between volume and 
superficial surface area. Deposition of carbonaceous materials by coke 
formation can also shift the effective ratio, as disclosed in U.S. Pat. 
No. 4,547,613. However, enhanced effectiveness is observed where the 
surface acid sites of small crystal zeolites are reacted with a 
chemisorbed trialkyl pyridine, such as collidine. 
It is a main object of this invention to provide an improved process for 
upgrading olefins to valuable lubricant quality product. Significantly 
improved linearity can be achieved by employing a catalyst comprising a 
medium pore shape selective siliceous zeolite with a surface that has been 
substantially inactivated with a sterically hindered nitrogenous base, 
such as a trialkyl pyridine compound. 
SUMMARY OF THE INVENTION 
It has been discovered that when a surface-inactivated, but internally 
active, ZSM-23 metallosilicate zeolite catalyst is employed in olefin 
oligomerization, the reaction yields a high quality, essentially linear 
oligomer stock which can be efficiently converted to high VI lube oils. 
The catalyst can be surface inactivated in situ by cofeeding a sterically 
hindered basic amine compound with the olefinic feedstock, or the novel 
catalyst can be treated in a separate step prior to olefin 
oligomerization. 
Unless otherwise specified, metric units and parts-by-weight (pbw) are 
utilized in the description and examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Recent developments in zeolite technology have provided a group of medium 
pore siliceous materials having similar pore geometry. Prominent among 
these intermediate pore size zeolites is ZSM-23, which may be synthesized 
with Bronsted acid active sites by incorporating a tetrahedrally 
coordinated metal, such as Al, Ga, or Fe, within the zeolitic framework. 
These medium pore zeolites are favored for acid catalysis; however, the 
advantages of ZSM-23 structures may be utilized by employing highly 
siliceous materials or crystalline metallosilicate having one or more 
tetrahedral species having varying degrees of acidity. ZSM-23 crystalline 
structure is readily recognized by its X-ray diffraction pattern, which is 
described in U.S. Pat. No. 4,076,842 (Rubin, et al.), incorporated by 
reference. 
The shape-selective oligomerization/polymerization catalysts preferred for 
use herein include the crystalline aluminosilicate zeolites having a 
silica-to-alumina molar ratio of at least 12, a constraint index of about 
8 to 10, and acid cracking activity (alpha value) of about 10-300. A 
suitable shape selective medium pore catalyst for fixed bed is a small 
crystal H-ZSM-23 zeolite having alpha value of about 25, with alumina 
binder in the form of cylindrical extrudates of about 1-5 mm. The 
preferred catalyst consists essentially of ZSM-23 having a crystallite 
size of about 0.02 to 2 microns, with framework metal synthesized as 
gallo-silicate, ferrosilicate, and/or aluminosilicate. These zeolites have 
a pore size of 4.5 X 5.6 Angstroms, such as to freely sorb normal hexane. 
In addition, the structure must provide constrained access to larger 
molecules. 
It is generally understood that the proportion of internal acid sites 
relative to external acid sites increases with larger crystal size. 
However, the smaller crystallites, usually less than 0.1 micron, are 
preferred for diffusion-controlled reactions, such as oligomerization, 
polymerization, etc. Accordingly, it may be required to neutralize more 
than 15% of the total Bronsted acid sites by chemisorption of the basic 
deactivating agent. 
The degree of steric hindrance should also be considered in the choice of 
the basic nitrogen compounds, especially the bulky trialkyl pyridine 
species having alkyl groups of 1 to 4 carbon atoms. Although the selected 
organonitrogen compound must be bulky enough to prevent infusion of said 
compound into the internal pores of the catalyst, excessive steric 
hindrance may prevent effective or complete interaction between the 
surface Bronsted acid site and the selected basic species. 
Catalysts of low surface activity can be obtained by using medium pore, 
shape selective ZSM-23 zeolites of small crystal size that have been 
deactivated by one or more trialkyl pyridine compounds, such as 
2,4,6-collidine (2,4,6-trimethyl pyridine, gamma-collidine). These 
compounds all must have a minimum cross-section diameter greater than the 
effective pore size of the zeolite to be treated; i.e., greater than 5 
Angstroms. 
EXAMPLE I 
Aluminosilicate H-ZSM-23 extrudate (65% zeolite, 35% alumina binder) is 
loaded into a metal pressurized reactor and calcined overnight at 
500.degree. C. The catalyst is then used to oligomerize propylene to 
intermediate molecular weight olefins. Various temperatures and feed rates 
are employed. These results are summarized in Table 1. 
TABLE 1 
______________________________________ 
Propylene Oligomerization with HZSM-23 
C.sub.12 + Branching 
Run Temp. Select. 
Branching 
Methyls.sup.b 
No. C.sub.3 .dbd. WHSV 
.degree.C. 
wt. %.sup.a 
Index.sup.b 
per C.sub.15 
______________________________________ 
1-A 1.0 160 61.5 51.7 3.7 
1-B 0.5 160 73.7 51.4 3.6 
1-C 0.5 200 78.6 54.7 4.0 
1-D 1.0 200 81.7 55.1 4.2 
1-E 1.0 225 78.5 52.3 3.9 
______________________________________ 
.sup.a In crude reaction product 
.sup.b In C.sub.12 + fraction 
The determination of Branching Index is a useful and sensitive method 
practiced by those skilled in the arts to which the present invention 
applies and used to quantitatively assess the degree of linearity of a 
molecule or molecular mixture. The index is determined as follows: the C6 
and C9 oligomers are first removed from the sample and the C12+ fraction 
is hydrogenated using Pd/charcoal catalyst in acetic acid. The 
hydrogenated sample is extracted from the acetic acid into 
deutrochloroform and the 1H NMR spectrum determined. The branching index 
is defined as the ratio of the intensity (area) of the resonance due to 
CH3 (0.7-1.0 ppm) divided by the sum of the intensities (areas) of the 
resonances due to CH3 (0.7.-1.0 ppm) and CH2 (1.1-1.8 ppm). The number of 
methyl groups per molecule is defined by the equation 
EQU Me/molecule=B.I.*(n+1))/150 
where B. I.=branching index as defined above and 
EQU n=carbon number of the fraction of interest. 
This calculated number of methyls per molecule includes the two terminal 
methyl groups. Therefore, to determine the actual number of mid-chain 
ethyl groups, these two terminal methyl groups must be subtracted from the 
total methyl/molecule value calculated. 
EXAMPLE II 
The catalyst used in Example I is calcined in the reactor overnight at 
500.degree. C. The calcined catalyst is then cooled to room temperature in 
the reactor, and a solution containing 1 gram 2,6-di-t-butyl pyridine per 
100 ml pentane is passed over the catalyst until a total of 6 ml of 
deactivating solution per gram of catalyst has been used. Following this 
treatment, the catalyst is purged with nitrogen for one hour at room 
temperature, then the reactor temperature is slowly increased and reaction 
of propylene begun. During the reaction of propylene, a small amount of 
2,6-di-t-butyl pyridine (DTBP) solution is co-fed to maintain surface 
deactivation. The results of these screening reactions are summarized in 
Table 2. 
TABLE 2 
__________________________________________________________________________ 
Propylene Oligomerization with 2,6-DTBP Modified ZSM-23 
C.sub.12 + Branching 
C.sub.3 .dbd. 
2,6-DTBP 
Temp. 
Select. 
Branching 
Methyls.sup.b 
Run No. 
WHSV 
ppm .degree.C. 
wt. %.sup.a 
Index.sup.b 
per C.sub.15 
__________________________________________________________________________ 
2-A 1.0 400 175 18.4 40.0 2.1 
2-B 0.5 800 200 43.8 39.4 2.3 
2-C 1.0 400 200 32.2 40.7 2.3 
2-D 0.5 800 220 50.4 41.9 2.6 
__________________________________________________________________________ 
.sup.a In crude reaction product 
.sup.b In C.sub.12 + fraction 
EXAMPLE III 
H-ZSM-23, prepared as in Example I is treated with deactivating solution as 
in Example II, except that the basic component is 2,4,6-collidine. A small 
co-feed of 2,4,6-collidine solution is continued during reaction to 
maintain surface deactivation. Results of these reactions are summarized 
in Table 3. 
TABLE 3 
______________________________________ 
Propylene Oligomerization with 
2,4,6-Collidine Modified ZSM-23 
2,4,6- C.sub.12 + Branching 
Run C.sub.3 .dbd. 
Coll., Temp. Select. 
Branching 
Methyls.sup.b 
No. WHSV ppm .degree.C. 
wt. %.sup.a 
Index.sup.b 
per C.sub.15 
______________________________________ 
3-A 0.5 200 200 24.7 35.5 1.8 
3-B 0.25 400 200 35.1 34.9 1.7 
3-C 0.25 400 212 39.7 37.2 2.0 
3-D 0.25 400 225 33.5 37.6 2.0 
3-E 0.25 200 225 36.4 40.4 2.3 
______________________________________ 
.sup.a In crude reaction product 
.sup.b In C.sub.12 + fraction 
The above experimental runs are conducted at a pressure of about 
3500-4300Pa (500-600 psig.). Comparative examples run at equivalent space 
velocity and temperature (e.g., 0.5 WHSV and 200.degree. C.) show 
significant improvement in product linearity employing the 
trialkylpyridine agent. 
EXAMPLE IV 
Propylene is contacted according to the procedure of Example I with 
2,4,6-collidine modified HZSM-23 in a flow reactor at 200.degree. C. at 
the rate of 0.25 g propylene/g zeolite/hr. The crude product is distilled 
to obtain a C.sub.15.sup.+ fraction. The C.sub.15 .sub.+ fraction is 
contacted with BF.sub.3 /70% aqueous phosphoric acid catalyst at room 
temperature for about 4 hours. The crude product, containing about 75 wt % 
of C.sub.25.sup.+ lube range hydrocarbon is stripped to remove the 
C.sub.24.sup.- hydrocarbons. The viscosity index of the C.sub.25.sup.+ 
fraction is 128; the 100.degree. C. viscosity is 8.2 cSt. 
In the multistage process 70% aqueous phosphoric acid in combination with 
BF.sub.3 is superior to other BF.sub.3 /promoter combinations for 
converting C.sub.10 -C.sub.20 intermediate olefins to lube-range 
hydrocarbons. 
While the invention has been described by specific examples and 
embodiments, there is no intent to limit the inventive concept except as 
set forth in the following claims. 
EXAMPLE V 
15.4 gms HZSM-5 (65% zeolite, 35% alumina binder) are treated with 0.18 
grams 2,4,6-collidine in approximately 50 cc pentane. This represents 0.25 
moles amine per mole of acid in the zeolite. The pentane is allowed to 
evaporate at room temperature and the surface modified catalyst charged to 
a fixed bed tubular reactor at superatmospheric pressure. Propylene is 
metered to the reactor and a solution of 1 gram 2,4,6-collidine in 500 ml 
pentane is also metered to the reactor. The rate is controlled to give 
approximately 0.2 mmoles amine per mole H+in the zeolite per hour. 
Reaction temperature is adjusted in an effort to achieve 50% propylene 
conversion. 
______________________________________ 
TEMP 205.degree. C. -PRESSURE 3600 kPa (500 psig) 
C3.dbd. WHSV, HR-1 0.21 
DEACTIVATING AGENT 
IN FEED 65 ppm 
C3.dbd. CONV, WT % 55.0 
C12+ SELECTIVITY 20.1% 
C15+ 5.9 
BRANCHING INDEX 32.8 
BRANCHING METHYLS 1.5 
PER C15 
______________________________________ 
EXAMPLE VI 
Example V is repeated, except that 15.4 gms ZSM-5 (65% zeolite, 35% alumina 
binder) are treated with a solution containing 0.28 grams, 
2,6-di-t-butylpyridine in pentane. (0.25 mols amine per mole H+ in the 
zeolite). Comparative results are summarized as follows: 
______________________________________ 
TEMP 145.degree. C. 
PRESSURE 3600 kPa 
C.sub.3.sup.= WHSV, HR.sup.-1 
0.22 
AMINE IN FEED 100 ppm 
C.sub.3.sup.= CONVERSION, WT % 
59.1 
C12+ SELECTIVITY 9.8 
BRANCHING INDEX 38.4 
BRANCHING METHYLS 2.1 
PER C15 
______________________________________ 
EXAMPLE VII 
Example V is repeated, except 15.4 gms HZSM-23 (65% zeolite, 35% alumina 
binder) are treated with 0.088 gms, 2,4,6-collidine in approximately 50 ml 
pentane. (0.25 moles amine per mole H+ in the zeolite). Screening is 
carried at various conditions with an effort to achieve 50% propylene 
conversion. Results are summarized as follows: 
______________________________________ 
TEMP 175.degree. C. 
PRESSURE 3600 kPa 
C3.dbd. WHSV, HR-1 0.21 
AMINE IN FEED 200 ppm 
C3.dbd. CONVERSION, WT % 
57.7 
C12+ SELECTIVITY 22.0 
BRANCHING INDEX 30.5 
BRANCHING METHYLS 1.25 
PER C15 
______________________________________ 
EXAMPLE VIII 
Example VII is repeated, except 15.4 gms ZSM-23 (65% zeolite, 35% alumina 
binder) are treated with 0.14 gms, 2,6-di-t-butylpyridine in approximately 
50 ml pentane. (0.25 moles amine per mole H+ in the zeolite). Results are 
summarized as follows: 
______________________________________ 
TEMP 145.degree. C. 
PRESSURE 3600 kPa 
C3.dbd.WHSV, HR-1 0.21 
AMINE IN FEED 50 ppm 
C3.dbd. CONVERSION, WT % 
59.0 
C12+ SELECTIVITY 21.6 
BRANCHING INDEX 31.4 
BRANCHING METHYLS 1.35 
PER C15 
______________________________________