Note: Descriptions are shown in the official language in which they were submitted.
~34~
FIELD OF THE INVENTION
This invention relates to an improvement in the
preparation of aromatic compounds. In particular, this
process relates to improving selectivity for benzene,
toluene and xylenes (BTX) in the liquid product obtained
using olefinic C2-C4 feedstocks passed over a ZSM-5
type catalyst.
.
RIOR ART
The conversion of hydrocarbons by contacting with solid
siliceous catalysts inrluding those re~erred to as
crystalline aluminosilicate zeolites has long been known in
the fi~ld. The contacting of hydrocarbons with the
aforementioned catalysts has been carried out for a wide
variety of reactions including cracking, isomerization and
hydrocracking. U.S. Patents disclosing and claiming these
processes are U.S. Patenk Nos. 3,140,249; 3,140,251;
3,140,253 and 3,140,322.
The contacting of hydrocarbon feeds with said catalysts
to obtain aromatics is also known in the field. These
procedures are described in U.S. Patent Nos. 3,760,024 and
4,304,657. These patents disclose contacting of C2-C4
olefins, paraffins and mixtures thereof with ZSM-S type
zeolites for conversion to aromatics.
- 2 ~
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The ~nstant application is concerned with the improvement of
benzene, toluene and xylenes selectivity in the liquid product upon
dilution of an olefin feed with Cl-C4 paraffins, when the dilution
results in particular mixed feeds, and the aromatization i9 carried out
under particular conditions, as set forth hereinafter.
Cattanach United States Patent 3,760,024 and Givens et al. United
States Patent 3,827,968 disclose production of aromatic hydrocarbons from
feed mixtures of C2 to C5 paraffinic and olefinic hydrocarbons with
H-ZSM-5 catalyst. Although mixed gases are disclosed as feeds,
experimental results are given only for pure propylene as feed and there
is no disclosure of particular mixed feeds and no disclosure that
mixtures give superior resul~s to pure propylene. There is no disclosure
of feedstocks containing methane.
Cattanach United States Patent 3,756,g42 discloses conversion of
normally liquid C5 plus hydrocarbons to aromatlc hydrocarbons over ZSM-5
type catalysts, discloses ~hat at 550C paraffins in the feed are
converted to aromatics, whereas at 390C the aromatics come primarily
from converting olefins to aromatics and discloses that lower temperatures
can be used with feeds containing paraffin and olefin hydrocarbons
than with a substantially paraffinic feed material. There is no
disclosure of normally gaseous feed materials, nor that at a given
temperature, conversion to aromatics i9 greater with paraffins and
olefins in the feed than with olefins alone.
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Givens et al United States Patent 3,960,978 discloses in Example
2 thereof aromatization of a mixture of methane, ethane, ethylene,
propane and propylene at 900-950F with Zn-HZSM-5 catalyst; the weight
ratio of olefin to paraffin is 2.3 to 1 and the mole ratio of olefin to
paraffin is 1.8 to 1; the weight ratio of olefin to methane is about
14.7 to 1, and the mole ratio of olefin to methane is about 5.9 to 1.
In Example 3 of this patent, a mixture of ethane, ethylene, propane and
propylene is aromatized at a temperature of 100F with Cr-HZSM-5
catalyst; the weight ratio of olefin to paraffin is 3.0 to 1 and the mole
ratio of olefin to paraffin is 2.8 to 1. There is no disclosure in this
patent of a mole ratio of olefin to paraffin less than 1.6 to 1, nor
of a mole ratio of olefin to methane less than 5.9 to 1, nor any
disclosure of any effect of the saturated hydrocarbons in the feed on
BTX production.
Garwood et al United States Patent 4,1501602 discloses conversion
f C2 to C4 olefins to high octane gasoline components including BTX at
temperatures up to 800F with ZSM-5 type catlayst, water being used as
diluent to control coking or aging of the catalyst and Cl to C4 saturated
hydrocarbons being disclosed as optional additional diluents. There is
no disclosure of temperatures above 800F (427C), nor of any effect
of the saturated hydrocarbon diluent on BTX production.
Miller U.S. Pate~t 4,304,657 discloses arcmatization of hydrocarbon
feedstock boiling in the range from C2 to 70C, containing paraffins
and/or olefins and/or naphthenes, diluted with carbon monoxide, carbon
dioxide or nitrogen, in order to decrease the hydrogen to methane mole
ratio of the product and decrease C10+ aromatics production. Experimental
results are given only for naphtha feedstocks and there is no disclosure
of a particular normally gaseous feedstoc3c other than propane. Ihere is
no disclosure that selectivity for BTX production is higher from gaseous
feeds when mixtures of paraffins and olefins are used. Ihere is no
disclosure of feedstocks containing methane.
~3~5~
SUMMARY OF THE INVENTION
The current invention provides for a process for converting an olefinic
feed to a product stream in which the liquid is comprlsed mainly of
benzene, toluene and xylenes, by contacting said feedstock with an
aromatization catalyst. This contact occurs at a temperature in the
range of 400 to 600C and a pressure of one atmosphere. The improvement
comprises diluting said feedstock with a diluent comprising Cl-C4
paraffins, at a mole ratio of feed to diluent ranging from 1:4 to 4:1.
The impro~ement results in an increase in the selectivity to benzene,
toluene and xylenes in the liquid product.
DETAILE~ DESCRIPTION OF THE PROPOSED EMBODIMENT
The present invention involves the contacting of a hydrocarbon stream,
consisting of C2-C4 olefins or mixtures thereof diluted with C1-G4
paraffins, or mixtures thereof, with an aromatization catalyst at a
temperature in the range of 400 to 600C to produce benæene, toluene and
xylenes.
The process of the invention is, as shown in the examples, capable of
produclng an aggregate weight percent yield of benzene, toluene and
xylenes, based on total liqu~d product, when a mixture of feedstock and
diluent i8 used, which is greater than that obtained in the absence of
diluent under otherwise similar conditions of catalyst, temperature,
pressure and total flow rate ~feedstock and diluent if any) per unit
. ~
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amount of catalyst. The process of the invention results in grea~er
selectiviey ~or conversion of feedstock to benzene, ~oluene or xylene,
and preferably in greater selectivity for the aggregate of benzene9
toluene and xylen~s.
The feedstock for this invention may be either a single oleinic species
diluted with a single paraffinic component or it may be a mixture of
olefins and diluents. Such mixtures may be those which are availa~le at
refineries, which are often used for internal heating within the plant.
In the latter case, after the process according to the invention, 80-90
wt% of the original gas stream may be returned for heating purposes and
at a higher H/C ratio.
The term 'aromatization catalyst' refers to ZSM-5 catalysts which are
capable of producing aromatics from a C2-C4 ole~inic feed. The ZSM-5
type of zeolite is generally considered to include ZSM-5, ZSM-8, ZSM-11,
ZSM-12 and other similarly behaving catalysts. U.S. Patent No. 3,702,886
describes methods o~ preparation of the ZSM-5 zeolites.
It is known in the art that zeolite~, particularly synthetic zeolites,
may have their compositions modified or altered by impregnation of
certain metals thereon or by exchanging variou~ anions and/or cations
into the crystal structure of the zeolite. The ZSM-5 family of catalyst
has been found to be especially active for aromatization if it has been
exchanged with ~he following cations: ammonium, chromium or nickel. In
particular the ammonium-exchanged ZSM-5 which results in the hydrogen
form upon calcination i8 preferred. Typically~ the exchange i8 achieved
. ~
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by contacting the sald zeolite with a salt of the desired replacing
cation. Although a wide variety of salts may be used partioular
preference is given to chlorides, nitrates and sulfates. It is also
known in the art to disperse the zeolite catalyst in a porous mixture
such as clay, alumina, silica and mixtures thereof. Techniques for
incorporating the zeolites into a matrix are set forth in U.S. Patent
No. 3,140,253.
In accordance with the present invention a feed of C2-C4 olefin or
mixture thereof is diluted with C1-C4 paraffins, or mixtures thereof and
contacted with an aromatizat~on catalyst. It ls preferred to use methane
as the diluent and H-ZSM-5 as the aromatization catalyst. The contact is
made at a temperature in the range of about 400~C to about 600C and
preferably 435C to 550DC., more pre~erably 460C to 510C. ~igher
temperatures favor selecti~ity for BTX, but if the temperature is too
high, the increase in selectivity will not ~ustify the higher energy
consumption.
Preferably, the reaction is conducted at atmospheric pressure; other
pressures can also be employed, but higher pressures may adversely affect
BTX yield and selectivity and are therefore not preferred. The feed to
diluent mole ratio is preferably in ~he range from abou~ 1:4 to about
4:1. When dlluents other than methane are used, the ratio should not be
greater than 2.4:1. Preferably the feed to diluent mole ratio is in the
range from about 1:2.5 to about 2.4:1. ~ligher ratios tend to reduce
yield and selectivity for BTX. Lower ratios, although they give good
yield and s~lectivity for BTX, increase the sl~e of equipment and the
.. ~
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amount of diluent required to be handled in processing of a given amount
of olefin hydrocarbon feedstock.
Preferably, the space velocity (~HSV) is at least three gra~s of total
feed per gram of catalyst per hour. Below that rate, coking of the
catalyst may increase. Higher space velocities can be employed; a person
skilled in the art can select suitable space velocities in the light of
the present specification.
Although the Cl to C4 hydrocarbons which are added to the feedstock in
the practice of the invention are refer~ed ~o as diluents, it is
understood that they may also enter into the reactions involved in the
process of the invention. The use of the term, diluent, does not
indicate that the material referred to is necessarily inert.
In the following examples 1,3,4 and 5 a stainless steel (316) reactor and
preheater were used. The tublng, from the cylinders to preheater inlee
and from condenser outlet was Teflon~ while all other tubing was
stainless steel. The preheater was a ~" OD s~ainless steel tube packed
to 4 inch depth with pyrex beads. A fixed-bed upflow reactor was used
with an axial thermowell. The catalyst in the reactor was supported by
plugs of quartz eape. Tubing between preheater and reactor, and reactor
and condenser was heated with an electrical heating tape. Pressure
gauges were mounted at the inlet to the preheater and the inlet to the
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reactor. The flow was monitored, controlled and mixed with a Matheson
Model No. 7352 flow controller equipped with No. 610A tubes.
In example 2 the system was similar except that the preheater was a ~ OD
stainless steel tube filled with pyrex beads with the gas flowing up, the
preheater outlet temperature was about 250 to 300C. The stainless steel
reactor was as in the other examples except that gas flow was down
through the reactor in example 2.
In the fol]owing examples, fresh catalyst samples were used in
Runs 4,5,14,17,22,28,32 and 35. In Run 7, a mixture of fresh and
regenerated catalyst was used. In the other runs, catalyst samples which
had been regenerated from one to eight times were used. The regeneration
procedure, performed after the completion of a run, and without cooling
from reaction temperature, is as follows:
Nitrogen is passed over the catalyst to purge the system. Then air is
passed o~er the catalyst at 30-40 mllmin. for 3-4 hours after which the
system is again purged with nitrogen. Hydrogen i~ then passed over the
catalyst at 10-15 ml/min. for 15-18 hours after which the catalyst is
ready for another run.
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Example 1
Th2 following runs illustrate the effects of dilution of the feed on the
selectivity to benzene, toluene and xylenes in the liquid product.
Selectivity is calculated as the weight percent of the aggregate of
benzene, toluene and xylene in the liquid product of the reaction. The
olefinic feed was propylene and the diluent was methane. The
propylene/methane mixture was contacted with a HZSM-5 catalyst at
atmospheric pressure. The dilution of the olefinic feed is seen to
improve the selectivity to benzene, toluene and xylenes. Dilution
changes the thermal profile in the reactor and, as a consequence, affects
the catalyst activi~y; these factors contribute to a favoring of benzene,
toluene and xylenes in the liquid product. The yields of benzene,
toluene and xylenes ~based on propylene in the feed) are also found to
increase. This is believed to be due to the combined effects of diluting
the stream with methane and of the contribution of methane as a reactant;
however, the invention is not to be limited by any theory as to the
reaction mechanism.
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Table 1
Propylene Feed Contacted
With H-ZSM-5 at AtmosF~ric Pressure With
and Without Methane _ luent
Runs 1-9 10 11 12 13
Diluent nonel CH4 CH4 CH4 CH4
Dilution (mol ratio of feed to diluent) 3:1 0.95:1 0.98:1 1:3
Reactor Temp (C) 527 530 523 496 518
WHSV (g olefin HC-(g cat) hr 1) 9.7 7.28 4.74 4.73 2.37
Catalyst leading (g) 0.5 0.5 0.5 0.5 0.5
Total Flow rate (ml/min.) 47.0 47.1 46.7 51.0 46.7
Yield
BTX Yield (wtX of C3H6 in) 26.0 36.7 37.8 24.2 36.8
BTX selectivity (wt~ of liquid)65.080.9 87.3 74.9 94.0
1. These pure propylene results are averages of 9 runs. The estimated
standard deviations of these averages are: temperature +16C, yields ~6.5
wt% and selectivity 110 wt%. The BTX selectivity range of extreme values
was 57 to 78 wt%. The data for the individual runs are as follows:
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Bed BTX BTX Liquid Total
Temp. Selectivity Yield Yield State of Flow
Run No. C wt % wt % wt ~Catalyst mL/min
1 543 74.2 26.2 35.2 R 47
2 541 77.6 32.0 41.3 R 47
3 538 68.3 23.6 34.7 R 47
4 541 59.3 23.3 39.3 F 47
520 77.8 32.8 42.2 F 48
6 499 59.7 21.8 36.4 R 47
7 504 47.2 15.0 32.0F(0.25g) 47
and
R(0.25g)
8 532 57.4 30.0 51.4 R 47
9 526 68.2 24.9 36.7 R 47
MEAN 527 65 26 38 47
STD DEV16 10 7 6
F - Fresh Ca~alyst
R = Regenerated Catalyst
Comparison of Runs 10,11 and 13 with Runs 1-9 shows that dilution of
propylene with methane increases the BTX yield and selectivity at
equivalen~ total flow rates per unit amount of ca~alyst and at generally
equivalent temperatures. The selectivity increases as the ratio of feed
to diluent decreases. In Run 12, the yield and selectivity were lower
than in Run 11, probably because of the lower temperature in Run 12.
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Example 2
The following runs further illustrate the effects of dilution of the feed
on the selectivity to benzene, toluene and xylenes in the liquid product.
The catalyst used ln these runs was prepared as followso
2.29 g SiO2 was dissolved in 17.7 mL of 25~ solution of tetrapropyl-
ammonium hydroxide. 0.32 g of NaA12O was dissolved in 2 mL of water.
These two solutions were combined and mixed well and then poured into a
pyrex tube. An additional 2 mL of water was used to wash residue out of
the beaker into the pyrex tube~ The tube was sealed and left for 7 days
at 170C. The solid was filtered, washed and dried at 110C overnight and
then calcined at 600C overnight. The catalyst was then determined to be
~SM-5 type by X-ray diffraction. The catalyst was ion exchanged in a
solution of 2M NH4NO3 (250 mL/g of catalyst) for 24 hours. The solid
was filtered, washed and dryed overnight at 110C and then calcined at
600C overnight.
The procedure was otherwise as disclosed in Example 1. Table 2 gives the
results obtained:
,
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Table 2
Propylene Feed Contacted with H-ZSM-5
at Atmospheric Pressure, With and Without
Methane Diluent
Runs 14 15 16 17 18 19
Diluentnone none CH~ CH4 CH4 CH4
Dilution (mol ratio
feed to diluent) - - 1.00:1 0.96:1 1.00:1 0.90:1
Reactor Temp (C)546 534 541 523 482 572
WHSV (g) o~efin ~C
(g. cat hr. ) 8.87 8.99 4.28 4.42 4,50 4.46
Catalyst loading (g) 0.5 0.5 0.5 0.5 0.5 0.5
Total flow rate
(ml/min) 43.0 43.6 41.5 43.6 43.5 45.9
BTX yield (wt.~
of C3H6 in) 17.1 19.3 29.5 24.9 24.3 34.8
BTX selectivity
(wt.~ of liquld) 51.8 61.3 74.6 80.2 80.2 91.2
Comparison of Runs 16, 17, 18 and 19 with Runs 14 and 15 again shows
superior BTX yield and selectivity at comparable temperature~ using
methane as diluent. Since the catalyst in Example 2 was from a different
batch from the catalyst used in Example 1, the results in Examples 1 and
2 are not directly comparable. For example, the lower yield and
selectivity in Run 17 as compared with Run 11 may be primarily the result
of the different catalyst used.
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In another run with the same caealyst as in Runs 16 to 19, with dilution
of 0.92:1, reactor te~perature of 433C, WHSV of 4.42, catalyst loading
of 0.5 and total flow rate of 44.1, BTX yield of 19.2 and BTX selectivity
of 60.9 were obtained, indicating the poorer results obt~ined with lower
reactor temperature.
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Example 3
The following runs illustrate the efEects of other dlluents on benzene,
toluene and xylenes seleceivity with propylene as the olefinic feed. The
feeds were contacted ~7ith the ~-ZSM-5 catalyst of Example 1, at
atmospheric pressure. The diluents, N2 and C3~8 (the latter in mole
ratios of feed to diluent of 0.91:1 and 0.31:1) improved the selectivity
to benzene~ toluene and xylenes compared to the undiluted stream. The
results for Runs 1-9 are included for comparison purposes.
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Table 3
Propylene/Propane and Propylene/Nitrogen
Feeds Contacted with H-ZSM-5 at Atmospheric Pressure
Runs 1-9 20 21 22 23
Diluent noneC3~8 C3H8 C3H8 2
Dilution (mol ratio of feed to diluent) - 0.91:1 3.03:1 0.31:1 0.90.1
Reactor Temp (C) 527 526 520 500 532
W~ISV (g olefinic ac- (g cat) l-hr 1) 9.7 4.547.26 2.32 4.75
Catalyst loading (g) 0.5 0.5 0.5 0.5 0.5
Total Flow rate (ml/min.) 47.0 46.2 46.847.4 48.5
Yield
BTX Yield ~wt% of C3H6 in) 26.0 29.7 15.327.6 28.0
BTX selectivity (wt70 of liquid) 65.0 75.457.7 83.2 73.2
Comparing Runs 20, 21 and 22 with Runs 1-9 indicates that superior yield
and selectivity for BTX are obtained with propane diluent as compared
with no diluent when the feed to d~luent mole ratio is about 1:1 (0.91:1)
and about 1:3 tO.31:1), but not when the ratio is about 3:1 (3.03:1).
Comparing Run 20 and 23 lndicates that propane and ni~rogen, as diluent,
give similar BTX yield and selectivity, with propane apparently somewhat
better. Comparing Run 23 with Run 11 in Example 1 indicates that methane
as diluent gives substantially increased B'FX yield and selectivity as
compared with nitrogen as diluentO
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Example 4
The following runs further illustrate the effects of paraffin hydrocarbon
diluents on benzene, toluene and xylenes se~ectivity with olefinic feeds
comprising ethylene and propylene. The feeds were contacted wlth H-ZSM-5
catalyst at atmospheric pressure. The feed composition was as follows:
Component Weight X
Oleflns
Ethylene 12.5 + 0.3
Propylene 24.4 + 0.5
Isobutene 3.46 + 0.07
1.3 - butadiene 0.51 ~ 0.01
Trans-2-butene 1.49 + 0.03
Cis-2-butene 1.32 + 0.01
43.6
Paraffins
Methane 0.085 ~ 0.002
Ethane 29.4 ~ 0.6
Propane 20.0 + 0.4
Isobutane L.65 + 0.03
n-butane 5.22 ~ 0.1
56.355
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The catalyst used was the same as in Example 1. The following results
were obtained. The results for Runs 1-9 wherein no paraffin hydrocarbons
were present, are shown for comparison.
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Table 4
C1 to C4 Olefin/Paraffin (P) Mixtures
Contacted with H ZSM-5 at Atmospheric Pressure
Runs 1-9 24 25 26 27
Diluent none P P P P
Dilution ~mol ratio of
C3H6 to diluent) - 0.74 0.74 0.74 0.74
Reactor Temp (C) 527 504 550 543 462
WHSV (g) o~efin ~C
(g. cat- hr.- ~ 9.7 3.59 3.5 3.5 3.5
Catalyst loading (g) 0.5 0.5 0.5 0.5 0.5
Total flow rate
(ml/min) 47.0 46.2 4409 44.9 44.9
BTX yield (wt.%
of olefin in) 26.0 28.3 35.B 32.5 24.2
BTX selectivity
(wt.% of liquid)65.068.3 82.6 72.9 69.8
Comparing Run~ 24, 25 and 26 wi~h Runs 1-9 indicates the superior yield
and selectivity obtained with the paraffin hydrocarbon dlluents. Run 27
gave lower yield and/or selectivi~y9 apparently because of lower reac~ion
temperature.
In additional runs with the catalyst used in Example 2, the following
results were obtained, the results for Runs 14 and 15 being shown for
comparison.
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Table 5
C~ to C4 Olefin/Paraffin (P) Mix~ures Contacted
with H-ZSM-5 at Atmospheric Pressur
Runs 14 15 28 29
Diluent none none P P
Dilution (mol ratio of feed to diluent) - - 0.74 0.74
Reactor Temp (C) 546 534 511 514
WHSV (g olefinic HC-(g cat) hr 1) 8.87 8.99 3.70 7.06
Catalyst loading (g) 0.5 0.5 0.5 0.5
Total Flow rate (ml/min.) 43.0 43.6 47.6 90.6
BTX Yield (wt% of C3H6 in) 17.1 19.3 18.3 17.7
BTX Selectivity (wt~ of liquid 51.8 61.3 64.4 55.7
.
Comparison of Runs 28 and 29 with Runs 14 and 15 indicates that compara~le
BTX yield and selectivity can be obtained at lower temperatures, with diluent as
compared to without diluent.
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Example 5
The following runs further illustrate the effects of paraffin hydrocarbon
diluents on benzene, toluene and xylenes selectivity with olefinic feeds
comprising ethylene and propylene. The feeds were contacted with HZSM-5
catalyst at atmospheric pressure.
The catalyst preparation was as follows: 1.37 grams of SiO2 was
pnrtially dissolved in 11.5 ml. of 25% tetrapropylammonium hydroxide
solution by heating to a temperature of about 100C. There was then
added a mixture of 0.19 grams NaAlO2 dissolved in 1.07 ml. of water.
The mixture was placed in a pyrex tube and sealed. The tube was heated
to l50C for 9 days. The resultant solid product was cooled to room
temperature, filtered3 washed with 2 liters of water and dried at 110C
overnight. A portion of this catalyst was analyzed by X-ray diffraction
and determined to be ZSM-5 type. The rest of the catalyst was calcined
at 600C overnight. The catalyst was then ion exchanged in 250 ml. of
2M NH4NO3 solution per gram of catalyst for 24 hours. The exchanged
catalyst was filtered, washed with distilled water, dried o~ernight at
110C and calcined at 600C overnight.
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The feed composition for Runs 32 and 33 was as follows:
Component Wei~ht %
Ethylene 3
Ethane 40
Propylene 17
Propane 40
The followin~ results were obtained. The results of Runs 30 and 31
wherein no paraffinic hydrocarbons were present, are shown for
comparison.
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Table 5
Cl to C4 olefin/paraffin (P) mixtures contacted
with H-ZSM-5 a~ atmos~heric pressure
Runs 30 31 32 33
Diluent none none P P
Dllution (mol ratio of C3H6 to diluent) - - 0.18 0.18
Reactor Temp (C) 552 565 552 565
WHSV (g ol~finic HC'(g cat) hr 1)9.71 9.71 2.28 1.69
Catalyst loading (g) 0.5 0O5 0.5 0.5
Total Flow rate (ml/min.) 47 47 64 47.3
BTX Yield (wtX of olefin in) 30.4 27.6 30.0 35.0
BTX selectivity (wt% of liquid 72.0 67.4 97.0 97.5
The results indicate an improvement in selectivity for BTX by use of the
paraffin diluents in Runs 32 and 33 as compared with Runs 30 and 31
respectively, and also an increase in BTX yield by use of the paraffin
diluents in Run 33, as compared with Run 31.
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