Note: Descriptions are shown in the official language in which they were submitted.
01 BE~NZENE SYNTHESIS
TECHNICAL FIELD
Benzene is one of the basic raw materials of
05 the chemical industry. It is used to synthesize rubbers,
dyes, and detergents and is also used as a solvent and as
an octane increasing gasoline additive. Benzene is
usually produced from hydrocarbonaceous feed materials in
a mixture with toluene, the xylenes, and higher aromatics
through reforming reactions such as cyclization, dehydro-
genation, and isomerization. A typical reforming process
uses straight-run naphtha feeds and platinum-containing
catalysts.
Recovery of purified benzene from the ben~ene-
toluene-xylene mixture requires some further treatment~
for example some combination of fractionation, solvent
extraction, and adsorptive extraction. The efficiency of
these separation steps increases as th~ benzene content of
the reformate increases~ Howe~ver, there has been no
particularly efficient process for producing a high-
benzene reformate which need not be fractionally
~istilled, solvent extract~d, or dealkylated to obtain a
high ben2ene content feed suitable for subsequent
purification steps.
The object of the present invention is to
provide such a process.
We have discovered that intermediate pore size
æeolitec can be used to convert light straight-run naph
thas (and similar mixtures) to highly aromakic mixtures.
Most surprisingly and unlike the product of traditional
reforming processes, the primary constit~ent of these
aromatic mixtures is benzene. Benzene synthesis using our
process becomes very much more eficient ~han processes
known to the art~ The importance of this development can
scarcely be overestimated in view of the increasing
> ~i~,~,'',
01 demands for benzene by the chemical and the autom~tive
industries, and in view of ~he decreasing amounts of
petroleum feeds available to the world market.
BACKGROUND ART
05 A number of V.S. patents which r~late to the
production of benzene/toluene/xylene (BTX) mixtures from
various feeds have issued.
U.S. 3,756,942, Cattanach, September 4, 1973
dis~loses the preparation of BTX from a C5 to 250F feed
using 2SM-5.
U.S. 3,760,024, Cattanach, September 18, 1973
discloses the preparation of C6+ aromatics from C2 to C~
para~fins or oleins using ZSM-5.
U.S. 3,77S,501, Kaeding, November 27, 1973
discloses BTX preparation from olefins using ZSM-5 in the
presence of oxygen.
U.S. 3,813,330, Givens, May 28, 1974 discloses
aromatizing olefins in the presence of easily cracked
paraffins to produce BTX using ZSM-5.
U.S. 3,827,968, Givens, August 6, 1974 discloses
a two step process for preparing 8TX from olefins using
ZSM-5. C2-C5 olefins are oligomerized to C5-Cg olefins
which are then aromatizedO
U.S. 3,843/7405 Mitchell, Octo~er 22, 1974
discloses the preparation of BTX using a two step process
and ZSM-5~
U.50 3,945,913, Brennan, March 23~ 1976
discloses the preparation of BTX from alkylaromatics
having nine or more carbon atoms.
U.S. 4,060,568, Rodewald, November 29, 1977
discloses the preparation of low molecular weight olefins
and p-xylene from alcohols using ZSM-50
U.S. 4,097,367t Haag, June 27, 1978 discloses
the preparation of BTX from olefinic naphthas and
~5 pyrolysis gasoline using ZSM-5.
.
01 U.S. 4,120,910, Chu, October 17l 1978 discloses
the preparation of C5+ aromatics and BTX by aromatizing
ethane~
U.S. 4,157,293~ Plank, June 5, 1979 discloses a
05 method for preventing the loss of zinc from Zn-ZSM-5
during the preparation of BTX from C~ to C10 paraffins and
olefins.
A survey of the background art shows a failure
to recognize the process of the present invention~ The
benzene content o the BTX products is typically much less
than 50%~
TECHNICAL DISCLOSURE
Our invention is embodied in a process for
selectively preparing a product havin~ a substantial
benzene content from normal and slightly branched chain
hydrocarbons, comprising:
(a) contacting a hydrocarbonaceous eed, which
comprises normal and slightly branched chain hydrocarbons
and has a boiling range above about 40C and below about
2.00C with a conversion catalyst which comprises an
intermediate pore si~e zeolite and a Group ~III metal
compound, and wherein said zeolite is substantially free
of acidity; and
(b) recovering a benzene containing effluent.
Feeds appropriate for use in the process contain
normal and slightly branched alkanes or olefins, or
: both. The feeds can also contain naphthenes. Because the
intermediate pore siæe zeolites used in the pro~ess are
shape selective, the efficiency of the conversion will be
greater the high~r the proportion in the fead of molecules
which can it within or par~ially within ~he zeolites.
Typical hydrocarbonaceous feedstocks appropriate for use
have a boiling range of above about 40C and below about
200C, preferably above about bOC and below about
120C. Normal feeds for refinery production of benzene
.
~1 include light straight-run fractions and light naphthas.
Paraffinic feeds, which are not efficiently dehydro-
cyclized by traditional reforming processes, can be
efficiently processed using our invention. Whatever the
S feed source, the higher the proportion of C6 and higher
alkanes and olefins in the feed, the greater the effi-
ciency of the process, and the higher the ben2ene content
of the effluent~ The most preferred feeds consist
essentially of hydrocarbons having from 6 to 8 carbon
atoms.
A particularly use~ul application of the present
process is in upgrading the effluent produced by
reforming. In typical reforming processes operating on
typical reforming feeds, the n-paraffins are unconvert-
ed. By using the reformer effluent as the feed in our
process for producing benzene, the aromatics content ofthe final reformate product can be substantially
increased; the octane rating of the product increases as
low octane n-paraffins are converted into high octane
benzene.
The intermediate pore size zeolites used in the
process are crystalline aluminosilicate zeolites having a
silica to alumina mole ratio greater than about 10:1 and
preferably greater than about 40:1. These zeolites have
useful activity even at high silica:alumina mole ratios
such as 1000 to 2000:1.
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 zeolite is in the ~-form.
Zeolites having pore apertures in this range tend to have
unique molecular sieving characteristics. Unlike small
pore zeolites such as erionite, they will allow hydro-
carbons having some branching into the 2eolitic void
spaces. Unlike large pore zeolites such as the
faujasites, they can differentiate between n-alkanes and
--5--
01 slightly branched alXanes on the one hand and larger
branched alkanes having, for example, quarternary carbon
atoms.
The effective pore size of the zeolites can be
05 measured using standard adsorption techniques and hydro-
carbonaceous compounds of known minimum kinetic diameters.
See Breck, Zeolite Molecular Sieves, 1974 (especially
Chapter 8) and Anderson et al., J. Catalysis 58, 114
(1979).
Intermediate pore size zeolites in the E~-form
will typically admit molecules having kinetic diameters of
5 to 6 Angstroms with little hindrance. Examples of such
compounds (and their kinetic diameters in Angstroms)
are: n-hexane (4.3), 3-methylpentane (5.5), benzene
(5.85), and toluene ~5.8). Compounds baving kinetic
diameters of about 6 to 6.5 Angstroms can be admitted into
the pores, depending on the particular zeolite, but do not
penetrate as quickly and in some cases, are effectively
excluded (for example, 2,2-dimethylbutane is excluded from
H-ZSM-5). Compounds having kinetic diameters in the range
of 6 to 6.5 Angstroms include: cyclohexane (6.0), 2,3-
dimethylbutane (6.1), ~,2-dimethylbutane (6.2), m-xylene
~6.1) and 1,2,3,4-tetramethylbenzene t6.4). Generally,
compounds having kinetic diameters of greater than about
~5 6,5 Angstroms cannot penetrate the pore apertures and thus
cannot be adsorbed in the interior of the zeolite.
Examples o such larger compounds include: o-xylene
~6.8), hexamethylbenzene (7.1), 1;3,5-trimethylbenzene
~7.5), and tributylamine (8~
3~ The preferred effective pore size range is from
about 5.3 to about 6.2 Angstroms. ZSM-5, ZSM-ll, and
silicalite, for example, fall within this range.
In performing adsorption measurements to deter-
mine pore size, standard techniques are used. It is
convenient to consider a particular molecule as excluded
- 6
if it does not reach a-t least 95~ of its e~uilibrium adsorption
value on the zPolite in less than about 10 minutes (P/Po = 0.5,
25C).
Examples of intermediate pore size zeolites include
silicalite and members of the ZSM series such as ZSM-5, ZSM-ll,
ZSM-12, ZSM-21, ZSM-23, ZS~-35, and ZSM-38.
ZS~-5 is described in United States Patents 3,702,886
and 3,770,614; ZSM-ll ls described in United States Patent
3,709,979; ZSM-12 is described in United States Patent
3,832,449; ZSM-21 is described in United States Patent
3,9'18,758; and silicalite is described in United States Patent
4,061,724. The preferred zeolites are silicalite, ZSM-5, and
ZSM-ll.
The conversion catalyst must include a Group VIII
metal compound to have sufficient activity for commercial use.
By Group VIII metal compound as used herein is meant the metal
itself or a compound -thereof. The Group VIII noble metals and
-their compounds, platinum, palladium, and iridium, or combina-
tions thereof can be used. The most preferred metal is platinum.
The Group VIII metal component can be impregnated into -the zeo-
lite after it is formed, or the metal can be included in the
reaction mixture from which the zeolite is hydrothermally
crystallized. It is highly desirable for the metal component
~o be dispersed uniformly throughout the zeolite, by inclusion
in the hydrothermal crystallization mixture for example~ The
amount of Group VIII metal present in the conversion catalyst
should be within the normal range of use in reforming catalysts,
from about 0.1 to 1.0 weight percent, preferably 0.2 to 0.8
weight percent, and most preferably 0.2 to 0.6 weight percent.
- 6a -
Reforming catalysts containing platinum are usually
subjected to halogen or halide treatments to achieve or maintain
a uniform metal dispersion and they also contain a halide
component (especially a chlorine
~a
94:~L
--7--
01 compound~. The catalysts of our invention can be
subjected to similar treatments without lessening the
catalytic specifici~y for benzene synthesis. The halide
treatment does not appear to have a significant effect on
05 the yield of benzene.
The intermediate pore siæe zeolite/Group VIII
metal conversion catalyst can be used without a binder or
matrix. The preferred inorganic matrix, where one is
used, is a silica-based binder such as Cab-O-Sil or Ludox.
Other matrices such as magnesia and titania can be used.
The preferred inorganic matrix is nonacidic.
It is critical to the selective production of
benzene in useful quan~ities that the conversion catalyst
be substantially free of acidity, for example by poisoning
the zeolite with a basic metalt e.g., alkali metal, com-
pound. Intermediate pore size zeolites are usually
prepared from mixtures containing alkali metal hydroxides
and thus have alkali metal contents of about 1-2 weiyht
percent. These high levels of alkali metal, usually
sodium or potassium, are unacceptable ~or most catalytic
applications because they cause a high fouling rate.
Usually, the alkali metal is removed to low levels by ion-
exchange with hydrogen or ammonium ions. By alkali metal
compound as used herein is meant elemental or ionic alkali
metals or their basic compounds. Surprisingly, unless the
zeolite itself is substantially free of acidity, the basic
compound is required in ~he present process to direct the
synthetic reactions to benzene production.
The amount of alkali metal necessary to render
the zeolite substantially free o acidity can be calcu-
lated using standard techniques based on the aluminum
conten~ of the zeolite. Under normal circumstances, the
zeolite as prepared and without ion-exchange will contain
sufficient alkali metal to neutralize ~he acidity of the
~atalyst. If a ~eoli~e free of alkali metal is the
.
01 starting material, alkali metal ions can be ion exchanged
into the zeolite to substantially eliminate the acidity of
the zeolite. An alkali metal content of about 100%, or
greater, of the acid sites calculated on a molar basis is
05 sufficient.
Where the basic metal content is less than 100%
of the acid sites on a molar basis~ the following test can
be used to determine if the zeolite is substantially free
of acidity. The test procedure is as follows: 0.1-0.59
of catalyst is mixed with lg of acid-washed and neutral-
ized alundum and packed in a 3/16" stainless steel reactor
tube with the remaining space filled with alundum. The
reactor contents are calcined for one hour at 450C. The
reactor is then placed in a clam shell furnace and the
lS reactor outlet connected to the inlet of a gas
chromatograph. The inlet is connected to the carrier yas
line of the GC. Helium is pa~sed through the system at 30
cc/min. 0.04 Microliter pulses of n-decane are injected
through a septum above the reactor and reaction products
are determined by standard GC analysis. ~lank runs with
alundum should show no conversion under the experimental
conditions, nor should a 100% Catapal alumina catalyst.
~ pseudo-first-order, cracking rate constant, k,
is calculated using the formula5
k = 1- ln
A l-x
where A is the weight of zeolite in grams and x is the
fractional conversion to products boiling ~elow decane.
The zeolite is substantially free of acidity when the
value for ln k is less than about -3.8.
The preferred alkali metals are sodium and
potassium. The zeolite itself can be substantially free
of acidity only at very high silica:alumina mol ratios; by
.
- 9 -
01 "zeolite consisting essentially of silica~ is meant a
zeolite which is substantially free of acidity without
base poisonlng.
The reaction conditions for the process typi-
05 cally include pressures ranging from atmospheric to 10bar, and liquid hourly space velocities (LHSV) ranging
from 0.1 to 15. If desired, hydrogen can be mixed with
the feed to lessen the tendency of the catalyst to foul,
but hydrogen need not be used. The reactions can take
place at ~emperatures above 480C. Surprisingly, the
process is most efficient at relatively high temperatures,
above 510C and ranging up to about 595C.
By substantial amount of benzene is meant a
benzene content of the C5+ aromatics produced which is
greater than about 50% by weight of the C5~ aromatics,
preferably greater than about 60% by weight, and most
preferably greater than about 75% by weight.
The following examples illustrate the invention.
All percentages given are ~y weight, unless otherwise
indicated.
Two light straight-run feeds were used in the
tests,
Feed 1
Gravity, API 79
~5 Nitrogen, ppm C0.1
Sulfur~ ppm <0.2
Vol. ~ paraffin 83.6
~istillation ~D86~ ~F:
Start/5 118/123
10/30 12~135
143
70/90 156/177
95/EP 194/297
--10--
01 Feed 2
Gravity, API 75
Nitrogen, ppm <0.1
Sulfur, ppm <0.02
05 Vol. % paraffin 77.2
Distillation (D86) F:
Start~5 120/133
10/30 136/1~7
157
70/90 170/198
95/EP 216/254
Example 1
A series of experiments were performed to
illustrate the necessity of using a zeolite substantially
free of acidity to produce benzene. In the first set of
experiments a zeolite prepared according to U.S. 4,061,724
and having a silica:alumina mole ratio of 89~:1 was
used. No inorganic matrix was used. Feed 2 was used as
were the following conditions: L~SV=l, no hydrogen, 3.4
~0 bar ~gau~e), and 538C~ Calculations show that 0.16%
sodium would saturate the acid (aluminum) sites.
Catalyst A B C _
Na level, ~ 0.017 0.99 4.12
Pt level, ~ 0.33 0.38 0.44
Product
C5+, % of feed 36.B8 79~69 85.59
Aromatics, % of C5+gl.60 56O43 42.57
Benzene, % of
aromatics 8.81 65.45 65.B9
These data $how that as the sodium level in-
crea~ed taS the acidity of the zeolite decreased and was
neutralized~ the yield of the C5~ fraction increased and
3~
3L~9~
01 the benzene content of the C5+ aromatics fraction in-
creased substantially.
A second set of experiments also showed the
surprising effect of an acid-free zeolite on benzene
05 specificity. Again using Feed 2, LHSV=l, H2/HC=1, 1.65
bar (gauge), and 538C together with zeolites exhibiting
the ZSM-5 X-ray diffraction pattern and having a
silica:alumina mole ratio of 121:1 (D and E), and, pre-
pared according to U.S. 4,061,724 ~; silica:alumina mol
ratio of 938:1), the following results were obtained:
Catalyst D E F
~Ja level ~ 2.D3 0.005 1.14
Pt % 0,44 0.34 0.36
Re % 0.42 0O37 0
Cl % 0.~9 <0.05 0
Product
C5~r % of ~eed 52.67 37.5~ 48.55
~ Aromatics, ~ of CS+ 88.63 92.05 92.82
Benzene, ~ of Aromatics 89.14 34.12 94.76
These data also illustrate the significant
selectivity towards ben~ene production of the present
invention.
Further experiments to show the selective
production of benzene in the aromatics fraction and the
effect of alkali metal poisoning were performed using a
; zeolite prepared according to U.S~ Patent 4,073~865,
Flanigen, February 14, 197~ and having an aluminum content
of 950 ppm (W/W). The reactions were performed on Feed 2
at LHSV=l, no hydrogen, 3O3 bar (gauge~, and 538C.
~9~
-12-
01 Catalyst G H
Na % 2.82 ~0.005
Pt % 0.49 0.24
05 Product
C5+ % of feed 83 55 43.61
Aromatics % of C5~ 15.47 63.43
Benzene, ~ of aromatics62~44 7~91
Although the aromatics fraction of the C5+
product of G is low, it has a high ben~ene content, and,
based on feed converted, G produced significantly more
benæene ~ca. 8%) than H (ca. 2.5%).
Example 2
Experiments were performed to show the necessity
of havin~ a Group VIII metal present to achieve not only
benzene selectivity but also reasonable yields of
aromatics. Feed 2 was used along with LHSV=l, 3.3 bar
~gauge), no hydrogen, and 538C. The zeolites of I
exhibited the X-ray dif~raction pattern o ZSM-5 while the
zeolite of J was prepared according to U.S. 4,061,724.
The ~eolites were not composited with an inorganic matrix.
Catalyst I _ J
SiO2:A12O3 67~4 892
Na % 1.02 0.99
Pt ~ o 0.
.
Product
C5+, % of eed 95.64 79.69
3 Aromatics~ ~ of ~5+ 3.24 66.43
Benzene, ~ aromatics 49.69 65.45
These data show that the ~roup VIIT metal,
platinum in this case, is necessary not only to yield a
3~ .
g43~
-13-
Dl high benzene fraction of the aroma~ics formed, but also to
yield practical amounts of an aromatic frac~ion.
Example 3
The preceding examples show ~hat benzene can be
05 selectively produced in high yields from zeolites having a
wide range of silica:alumina mole ratios. Several further
experiments were also performed to illustrate this
activity. The catalyst of ~ was prepared according to
U.S. 4,061,724 while that of L exhibited the ZSM-5 X-ray
diffraction pattern~ Reaction conditions included 1.65
bar (gauge), H2/HC=l, LHSV=l, and 538C.
Feed #1 #2
Catalyst ~ L
Silica:Alumina 938 121
Na ~ 1.14 2.03
Pt % 0.35 0.44
Re ~ 0.54 0.42
Cl % 0.
Product
C5~ ~ of feed 47.43 52.67
Aromatics, % of C5~ 100 88.63
Ben~ene~ ~ of aromatics 87~73 89.14
Example 4
Feed ~2 was processed with a platinum (0.3Ç%),
sodium (1.14%) zeolite prepared according to U.S.
4,061,7~4 and having a silica:alumina mole ratio of
938:1. The reaction conditions included LHSV=l, 1.65 bar
~gauge), H~HC~l, and 538~C. The products were compared
at the beginning and end of the run.
-14-
01 Beginning End
~after (after
1 hour) 20 hours)
C5+, % oE feed 57.63 80.48
05 Aromatics~ % of C5+ 87.30 57.78
Benzene, % of aromatics 85.2 75.2
% of feed 42.86 35.89
C7+ aromatics~ % of feed 7.45 11.60
Unconverted feed 7.D5 33.97
These data illustrate the surprising result,
that as the catalyst fouls, the yield of C5~ increases,
benzene remains a major component of the C5~ aromatics,
benzene remains a major product, and non-benzene aromatics
remain a minor portion of the product. The sites which
have undesirable cracking activity foul faster than ~he
benzene synthesis sites.
Example 5
According to the dehydrocyclization mechanism
through which conventional reforming proceeds, an
n-heptane feed would yield a product which is primarily
toluene, with only small amounts of ben2ene and other
aromatics. An experiment was performed using an n-heptane
. feed, a platinum, sodium ZSM-5 zeolite and L~SV-l, 1.65
bar ~gauge), H~/HC=lt and 538C. The data from the begin-
2~ ning and end of the experiment show significant amounts of
ben~ene are produced from n-heptane.
Beginning End
~after (after
1 hour~ ~0 hours)
C5+, ~ of feed . 58.98 69.26
Aromatics~ % of C5~ 94.87 84.32
Benzene, % of feed 39.40 21.99
C7~ aromatic~ ~ of feed 16.56 36.41
Un~onverted feed 1.92 3~65
~g~9~1
01 Example 6
An experiment was performed using Feed ~2 and a
2eolite exhibiting the ZSM-5 X-ray diffraction pattern.
The alkali metals were sodium (in M) and potassium ~in
05 N). Reaction conditions included 3.3 bar (gauge), no
hydrogen, LHSV=l, and 538C.
Catalyst M N
Cation level, % 0.99 1.46
Pt, % 0.38 0.3~
C5+, % of feed 79.69 68.59
Aromatics, of C5+66.43 40.08
Benzene, % of aromatics 65.4S 76.67
Closure 98.77 89~50
These data indicate that an aromatics fraction
with a high benzene content can be prepared from a zeolite
whose acidity is neutrali2ed by different alkali metals.
Example_7
An experiment was performed using Feed #l and a
zeolite prepared according to U.S. 4,061,724 to show the
effect of halide on the content of the Cl to C4 gas. The
catalysts were unbound.
Catalyst O P
~5 Cl, % 0.7~ 0
Pt, ~ ~.35 0.48
Re, ~ ~ 54
Na, ~ 1.14 1.14
-16-
01 Product Yield
C5+, % 47.43 70.18
Aromatics, ~ of C5+ 100 52.22
Benzene, % of C5+
05 aromatics 87.73 77.10
Methane, wt % of feed55.62 11.98
C2 0 ~97
C3 5.35
C4 .7.24
The test shows the selective production of
methane as opposed to the other light gases.
~5
: 3~
