Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By isomerization
Reexamination Certificate
2000-11-03
2002-05-14
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By isomerization
C585S482000
Reexamination Certificate
active
06388159
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for isomerizing xylenes using a family of related crystalline aluminosilicate zeolites examples of which have been designated UZM-5, UZM-5P and UZM-6. These compositions are structurally different from other known zeolites.
BACKGROUND OF THE INVENTION
Zeolites are crystalline aluminosilicate compositions which are microporous and which have a three-dimensional oxide framework formed from corner sharing AlO
2
and SiO
2
tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared are used in various industrial processes such as hydrocarbon conversion processes. One particular process which uses zeolites as a catlyst is the isomerization of aromatic compounds, especially the isomerization of C
8
aromatic compounds. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure.
Catalysts for isomerization of C
8
aromatics ordinarily are classified by the manner of processing ethylbenzene associated with the xylene isomers. Ethylbenzene is not easily isomerized to xylenes, but it normally is converted in the isomerization unit because separation from the xylenes by superfractionation or adsorption is very expensive. A widely used approach is to dealkylate ethylbenzene to form principally benzene while isomerizing xylenes to a near-equilibrium mixture. An alternative approach is to react the ethylbenzene to form a xylene mixture via conversion to and reconversion from naphthenes in the presence of a solid acid catalyst with a hydrogenation-dehydrogenation function. The former approach commonly results in higher ethylbenzene conversion, thus lowering the quantity of recycle to the para-xylene recovery unit and concomitant processing costs, but the latter approach enhances xylene yield by forming xylenes from ethylbenzene. A catalyst composite and process which enhance conversion according to the latter approach, i.e., achieve ethylbenzene isomerization to xylenes with high conversion, would effect significant improvements in xylene-production economics.
Applicants have synthesized a family of crystalline zeolitic compositions which have unique x-ray diffraction patterns and have the empirical formula on an anhydrous basis in terms of molar ratios of:
M
m
n+
R
r
p+
Al
(1−x)
E
x
Si
y
O
z
where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, “m” is the mole ratio of M to (Al+E) and varies from about 0 to about 1.2, R is a nitrogen-containing organic cation selected from the group consisting of quaternary ammonium ions, protonated amines, protonated diamines, protonated alkanolamines, quaternary alkanolammonium ions and diquaternary ammonium ions, and mixtures thereof, “r” is the mole ratio of R to (Al+E) and has a value of about 0.25 to about 3.0, E is an element selected from the group consisting of Ga, Fe, Cr, In and B, “x” is the mole fraction of E and varies from 0 to about 0.5, “n” is the weighted average valence of M and has a value of +1 to about +2, “p” is the weighted average valence of R and has a value of +1 to about +2, “y” is the mole ratio of Si to (Al+E) and varies from about 5 to about 12. and “z” is the mole ratio of O to (Al+E) and has a value determined by the equation:
z=(m·n+r·p+3+4·y)/2.
Specific members of this family of zeolites are: UZM-5, UZM-5P and UZM-6.
SUMMARY OF THE INVENTION
This invention relates to a process for isomerizing aromatic compounds using a new family of zeolites. Accordingly, one embodiment of the invention is a process for the isomerization of a non-equilibrium feed mixture of xylenes and ethylbenzene comprising contacting the feed mixture in the presence of hydrogen in an isomerization zone with a catalyst composite comprising an effective amount of at least one platinum-group metal component and an aluminosilicate crystalline zeolite at isomerization conditions to obtain an isomerized product comprising a higher proportion of p-xylene than in the feed mixture, the zeolite having a composition in the as synthesized form in terms of mole ratios of the elements given by:
M
m
n+
R
r
p+
Al
(1−x)
E
x
Si
y
O
z
where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, “m” is the mole ratio of M to (Al+E) and varies from about 0 to about 1.2, R is a nitrogen-containing organic cation selected from the group consisting of protonated amines, protonated diamines, protonated alkanolamines, quaternary ammonium ions, diquaternaryammonium ions, quaternized alkanolamines and mixtures thereof, “r” is the mole ratio of R to (Al+E) and has a value of about 0.25 to about 3.0, E is at least one element selected from the group consisting of Ga, Fe, Cr, In and B, “X” is the mole fraction of E and varies from 0 to 0.5, “n” is the weighted average valence of M and has a value of about +1 to about +2, “p” is the weighted average valence of R and has a value of +1 to about +2, “y” is the mole ratio of Si to (Al+E) and varies from about 5 to about 12 and “z” is the mole ratio of O to (Al+E) and has a value determined by the equation:
z=(m·n+r·p+3+4·y)/2
the material characterized in that it has at least two x-ray diffraction peaks, one at a d-spacing of 3.9±0.12 Å and one at 8.6±0.2 Å.
Isomerization conditions comprise a temperature of about 1000 to about 500° C., a pressure of about 1 to about 50 atmospheres, a liquid hourly space velocity from about 0.5 to 10 hr
−1
and a hydrogen-to-hydrocarbon mole ratio from about 0.5:1 to 25:1.
In a particular embodiment, the zeolite catalyst has been designated UZM-5 and has the x-ray diffraction pattern having at least the d-spacings and intensities set forth in Table A:
TABLE A
UZM-5
2-&thgr;
d(Å)
I/I
o
%
6.31-5.89
14.00-15.00
w-m
7.96-7.58
11.10-11.65
m-s
10.40-10.01
8.50-8.83
w-m
12.11-11.59
7.30-7.63
m
16.10-15.53
5.50-5.70
m-vs
19.28-18.55
4.60-4.78
w-m
22.26-21.60
3.99-4.11
m
23.20-22.43
3.83-3.96
w-s
24.16-23.33
3.68-3.81
vs
30.48-29.55
2.93-3.02
w-m
31.94-30.92
2.80-2.89
w-m
44.83-43.47
2.02-2.08
w
This and other objects and embodiments will become more apparent after the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
One essential aspect of the process of the invention is a new family of zeolites. Three species have been designated UZM-5, UZM-5P and UZM-6. In its as-synthesized form, these zeolites have a composition on an anhydrous basis that is represented by the formula:
M
m
n+
R
r
p+
Al
(1−X)
E
x
Si
y
O
z
.
M is an exchangeable cation and is selected from the group consisting of alkali and alkaline earth metals. Specific examples of the M cations include but are not limited to lithium, sodium, potassium, cesium, strontium, calcium, magnesium, barium and mixtures thereof. The value of “m” which is the mole ratio of M to (Al+E) varies from 0 to 1.2. R is a nitrogen containing organic cation and is selected from the group consisting of protonated amines, protonated diamines, protonated alkanolamines, quaternary ammonium ions, diquaternary ammonium ions, quaternized alkanolammonium ions and mixtures thereof. The value of “r” which is the mole ratio of R to (Al+E) and varies from about 0.25 to about 3.0. The value of “n” which is the weighted average valence of M varies from +1 to about +2. The value of “p”, which is the average weighted valence of the organic cation has a value from about +1 to about +2. E is an element which is present in the framework and is selected from the group consisting of gallium, iron, boron, chromium, indium and mixtures thereof. The value of
Chen Qianjun
Jan Deng-Yang
Lewis Gregory J.
Miller Mark A.
Moscoso Jaime G.
Dang Thuan D.
Molinaro Frank S.
Tolomei John G.
UOP LLC
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