Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By contact with solid sorbent
Reexamination Certificate
2002-03-01
2004-01-06
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By contact with solid sorbent
C585S831000
Reexamination Certificate
active
06673979
ABSTRACT:
FIELD OF THE INVENTION
The invention is a process for separating C
8
alkylaromatic hydrocarbons from C
9
and C
10
alkylaromatic hydrocarbons.
BACKGROUND OF THE INVENTION
C
8
alkylaromatic hydrocarbons are generally considered to be valuable products, and para-xylene in particular is in high demand. On the other hand, C
9
and C
10
alkylaromatic hydrocarbons are not nearly as valuable but are typically produced as a byproduct in the same aromatic production processes used to produce C
8
alkylaromatic hydrocarbons. Various approaches have been used to convert the less valuable C
9
and C
10
alkylaromatic hydrocarbons into C
8
alkylaromatic hydrocarbons. One popular approach has been to transalkylate C
9
and C
10
alkylaromatic hydrocarbons along with benzene or toluene to form the C
8
alkylaromatic hydrocarbons. Specifically, trimethylbenzenes and tetramethylbenzenes have been transalkylated along with benzene and toluene to form xylenes. However, transalkylation reactions are equilibrium limited and the product contains a mixture of unreacted C
9
and C
10
alkylaromatic hydrocarbons along with the desired C
8
alkylaromatic hydrocarbons. To increase conversion, commercial processes have utilized a two-stage design with the first stage being a fixed bed reactor and the second stage being a separation unit. Unreacted C
9
and C
10
alkylaromatic hydrocarbons present in the reactor product stream are separated and recycled to the reactor; see for example U.S. Pat. No. 3,211,798 B1.
Once the C
8
alkylaromatic hydrocarbons have been produced, they may need to be separated from the unreacted C
9
and C
10
alkylaromatic hydrocarbons. The present invention provides a process for separating the desired C
8
alkylaromatic hydrocarbons from the less desired C
9
and C
10
alkylaromatic hydrocarbons using zeolite Y, or ion exchanged zeolite Y as an adsorbent. Zeolite Y has been used as an adsorbent in other applications such as the separation of the specific C
8
alkylaromatic hydrocarbon isomers. For example, U.S. Pat. No. 4,255,607 B1 discloses the separation of aromatic C
8
isomers by adsorption, preferably contacting the mixture with zeolite Y and then developing the resulting adsorption band with an ether having selectivity for para-xylene. Japanese Patent No. 79,037,129-B discloses contacting a mixture of C
8
aromatic hydrocarbons with a Y-type zeolite containing sodium, calcium, cobalt and or strontium as cation to selectively adsorb meta-xylene. U.S. Pat. No. 4,079,094 B1 discloses separating ethylbenzene from a mixture of xylene isomers by passing through a column of an adsorbent comprising type X or Y zeolite completely exchanged with strontium and potassium. The xylenes are selectively adsorbed and an ethylbenzene stream is withdrawn. U.S. Pat. No. 4,028,428 B1 discloses separating ethylbenzene from a mixture of xylene isomers by contacting the mixture with an adsorbent of a strontium-exchanged type X or type Y zeolite. The xylenes are selectively adsorbed and ethylbenzene may be withdrawn. U.S. Pat. No. 3,998,901 B1 discloses separating ethylbenzene from a mixture of xylene isomers under adsorption conditions with a type X or Y zeolite completely exchanged with strontium and potassium. U.S. Pat. No. 3,997,620 B1 discloses para-xylene being separated from mixtures containing other C
8
aromatics by contacting the mixture under adsorption conditions with type X or Y zeolite containing barium and strontium which selectively adsorbs the paraxylene.
The present invention solves a different problem from that of separating C
8
alkylaromatic hydrocarbon isomers. Instead, the present invention is directed to separating at least one C
8
alkylaromatic hydrocarbon from at least one C
9
or C
10
alkylaromatic hydrocarbon, which is a problem encountered in processes such as transalkylation. U.S. Pat. No. 4,956,552 B1 teaches that p-ethyltoluene may be separated from a mixture comprising p-ethyltoluene and at least one other component selected from C
8
alkylaromatic hydrocarbons and other C
9
aromatic hydrocarbons by contacting the mixture with zeolite Y ion exchanged with potassium. The p-ethyltoluene is selectively adsorbed and a raffinate stream containing the less strongly adsorbed alkylaromatic hydrocarbons is produced. The zeolite Y ion exchanged with potassium is contacted with a desorbent comprising 1,2,3,4-tetrahydronaphthalene or lower alkyl derivative thereof or an alkyl derivative of naphthalene at desorption conditions to effect the removal of p-ethyltoluene from the adsorbent as an extract stream. Applicants have discovered that in addition to zeolite Y ion exchanged with potassium, sodium zeolite Y as synthesized, without ion exchange, is effective to separate at least one C
8
alkylaromatic hydrocarbon from at least one C
9
or C
10
alkylaromatic hydrocarbon having at least one methyl or ethyl group, or a mixture thereof. Similarly, applicants have found that dealuminated sodium zeolite Y is successful in the claimed separation.
SUMMARY OF THE INVENTION
The purpose of the invention is to separate at least one C
8
alkylaromatic hydrocarbon from at least one C
9
or C
10
alkylaromatic hydrocarbon. The invention involves contacting a mixture containing (I) at least one C
8
alkylaromatic hydrocarbon and (II) at least one C
9
or C
10
alkylaromatic hydrocarbon having at least one methyl or ethyl group, or a mixture thereof, with dealuminated zeolite Y having a SiO
2
/Al
2
O
3
ratio in the range of from about 7 to about 25 and containing essentially sodium in the ion-exchangeable sites to selectively adsorb the C
9
or C
10
alkylaromatic hydrocarbon. The C
9
and/or C
10
alkylaromatic hydrocarbon(s) are more strongly adsorbed by the adsorbent relative to the C
8
alkylaromatic hydrocarbon. The C
8
alkylaromatic hydrocarbon may pass through the adsorbent or if weakly adsorbed, may be desorbed using a desorbent and is collected. The more strongly adsorbed C
9
, C
10
, or mixture of C
9
and C
10
alkylaromatic hydrocarbon(s) is desorbed using the desorbent and collected. In a more specific embodiment of the invention, the desorbent is selected from toluene, benzene, or a mixture thereof. In another more specific embodiment of the invention, the adsorbent is dealuminated zeolite Y having a SiO
2
/Al
2
O
3
ratio in the range of from about 7 to about 12.
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Bricker Maureen L.
McGonegal Charles P.
Zinnen Herman A.
Maas Maryann
Molinaro Frank S.
Tolomei John G.
UOP LLC
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