Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By contact with solid sorbent
Reexamination Certificate
1999-11-01
2001-08-14
Knode, Marian C. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By contact with solid sorbent
C585S831000
Reexamination Certificate
active
06274784
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. 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.
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 discloses the separation of aromatic C
8
isomers by adsorption, preferably contacting the mixture with zeolite Y and then developing the resulting adsorption bond 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 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 discloses separating ethylbenzene from a mixture of xylene isomers by contacting the mixture with an adsorbent of a strontiumexchanged type X or type Y zeolite. The xylenes are selectively adsorbed and ethylbenzene may be withdrawn. U.S. Pat. No. 3,998,901 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 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 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.
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 an adsorbent selected from (I) zeolite Y ion exchanged with a metal selected from the group consisting of calcium, sodium, strontium, a Group IB element, a Group VIII element, and mixtures thereof, (II) zeolite Y, and (Ill) combinations thereof to adsorb a C
8
alkylaromatic hydrocarbon and a 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 adsorbed C
8
alkylaromatic hydrocarbon is desorbed using a desorbent and is collected. The 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.
REFERENCES:
patent: 3943183 (1976-03-01), Rosback
patent: 4051192 (1977-09-01), Neuzil et al.
patent: 4956522 (1990-09-01), Zinnen
Bricker Maureen L.
McGonegal Charles P.
Zinnen Herman A.
Dang Thuan D.
Knode Marian C.
Maas Maryann
Molinaro Frank S.
Tolomei John C.
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