Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By alkyl or aryl transfer between molecules – e.g.,...
Reexamination Certificate
2001-06-25
2003-02-11
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By alkyl or aryl transfer between molecules, e.g.,...
C585S481000
Reexamination Certificate
active
06518471
ABSTRACT:
This invention is directed to a process for the selective production of meta-diisopropylbenzene (DIPB).
BACKGROUND OF THE INVENTION
Meta-DIPB is an important intermediate in organic synthesis. Thus resorcinol can be prepared by oxidizing meta-DIPB with air and then decomposing the resulting dihydroperoxide with acid. However, although para-DIPB can be separated from a mixture of PIDB isomers by super fractionation, the boiling points of ortho- and meta-DIPB are too close to allow effective separation of meta-DIPB by fractionation. Moreover, ortho-DIPB is not readily oxidized and hence builds up in the production loop, requiring removal as a purge and representing a yield loss. Thus, to be commercially viable, any process for producing meta-DIPB must minimize the production of the ortho-isomer.
Currently, meta-DIPB is manufactured commercially by alkylating cumene with propylene over a homogeneous AlCl
3
catalyst. The high activity of the AlCl
3
catalyst produces a mixture of DIPB isomers with near equilibrium ortho content. This is advantageous since at equilibrium in the liquid phase between 50 and 150° C. the ratio of meta:ortho DIPB is greater than 100 providing sufficient purity for efficient downstream conversion to resorcinol. Process operation between 50 and 150° C. also results in DIPB products containing less than 1000 ppm of co-boiling n-propyl-isopropylbenzene and trimethylindane impurities. However, corrosion and the need to neutralize, separate and recycle the AlCl
3
catalyst, make this process difficult to practice.
DIPB can also be produced by separation from the polyalkylated by-product of the alkylation of benzene with propylene to produce cumene over a heterogeneous catalyst, such as a molecular sieve. However, DIPB separated from the polyalkylated fraction of current commercial cumene plants is rich in the kinetically preferred para- and ortho-DIPB isomers, making this route of limited use in the synthesis of meta-DIPB, unless the ortho- and para-content is reduced by, for example, isomerization or transalkylation. Transalkylation and isomerization, however, can introduce contaminant n-propyl-isopropylbenzenes and trimethylindanes.
Accordingly, there is an outstanding need for a heterogeneous process for producing high purity DIPB's near their equilibrium distribution (rich in the meta-isomer and substantially free of the ortho-isomer and impurities such as n-propylisopropylbenzenes and trimethylindanes.)
U.S. Pat. No. 4,992,606 discloses a process for preparing short chain (C
1
-C
5
) alkylaromatic compounds by alkylation of an aromatic compound, such as benzene and cumene, with a short chain alkylating agent, such as propylene, over the molecular sieve MCM-22. In addition, U.S. Pat. No. 4,962,257 discloses the use of MCM-22 in the disproportionation of toluene to xylenes.
U.S. Pat. No. 5,329,059 discloses a process for the disproportionation of an alkylaromatic compound, wherein the alkyl group has from 1 to about 6 carbon atoms, e.g., cumene, by contacting said compound with catalyst comprising an active form of synthetic porous crystalline MCM-49. MCM-49 is one of a family of molecular sieves which, together with MCM-36 and MCM-56, have certain structural similarities with MCM-22.
U.S. Pat. No. 4,822,943 discloses a process for the selective production of para-DIPB by reacting cumene and/or benzene with propylene over the molecular sieve ZSM-12.
U.S. Pat. No. 5,198,595 discloses a process for preparing alkylaromatic compounds by alkylation of an aromatic compound with an alkylating agent having two to eighteen carbon atoms, such as propylene, over mordenite which has been subjected to repeated calcination and acid treatment so as to have a silica/alumina molar ratio of at least 40:1.
U.S. Pat. No. 6,049,018 discloses the porous crystalline material MCM-68 and its use in the alkylation of aromatics with short chain (C
2
-C
6
) olefins (for example, the alkylation of benzene with ethylene or propylene to produce ethylbenzene or cumene respectively), the transalkylation of aromatics (for example, the transalkylation of polyethylbenzenes or polyisopropytbenzenes with benzene to produce ethylbenzene or cumene respectively), and the disproportionation of alkylaromatics (for example, the disproportionation of toluene to produce xylenes).
U.S. Pat. No. 3,780,123 discloses the catalytic disproportionation of alkylbenzenes, including cumene, by contacting the alkylbenzene and a sulfide compound with hydrogen mordenite containing a sulfided Group VIII metal. According to Table 1 of U.S. Pat. No. 3,780,123, when mordenite is used to disproportionate cumene in the presence of methyldisulfide as the sulfide compound, the process produces a mixture of DIPB isomers in which the meta:ortho isomer ratio is between 58 and 85 and the product contains 4.4-7.2 wt % n-propylbenzene and 4.4-5.2 wt % of unidentified impurities. As a co-boiler with cumene, n-propylbenzene is an undesirable impurity, particularly since, on disproportionation, it yields n-propylisopropylbenzenes which tend to co-boil with meta-DIPB.
It will, of course, be understood that the disproportionation of cumene to produce DIPB and benzene is the inverse of the transalkylation of DIPB with benzene to produce cumene.
According to the invention, it has now been found that if a mixture of DIPB isomers, such as that produced by a commercial cumene plant, is contacted under conversion conditions with benzene, either alone or in combination with cumene, in the presence of a molecular sieve selected from an MCM-22 family molecular sieve, zeolite beta and mordenite, the ortho-DIPB and/or the para-DIPB in the mixture are selectively converted. Depending on the composition of the feedstock the conversion occurs by transalkylation or a combination of transalkylation and isomerization. As a result, the process of the invention provides a heterogeneous route to the production of a meta-rich DIPB product in which the meta:ortho ratio is in excess of 100, and preferably in excess of 200. Moreover, the production of impurities which coboil with meta DIPB is very low, typically less than 0.5 wt % of the DIPB product.
SUMMARY OF THE INVENTION
In one aspect, the invention resides in a process for the selective production of meta-diisopropylbenzene, said process comprising the steps of:
(a) contacting a C
9
+ aromatic hydrocarbon feedstock containing meta-and ortho-diisopropylbenzene with benzene under conversion conditions with a catalyst comprising a molecular sieve selected from the group consisting of zeolite beta, mordenite and a porous crystalline inorganic oxide material having an X-ray diffraction pattern including the d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstrom, said contacting step selectively converting ortho-diisopropylbenzene in the feedstock to produce an effluent in which the ratio of meta-diispropylbenzene to ortho-diispropylbenzene is greater than that of the feedstock; and then
(b) feeding said effluent to a separation zone to recover from said effluent a product rich in meta-diisopropylbenzene.
Preferably, said porous crystalline inorganic oxide material is selected from the group consisting of MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49 and MCM-56.
Preferably, said porous crystalline inorganic oxide material is MCM-22.
Preferably, said feedstock is contacted in step (a) with benzene and cumene.
Preferably, said conversion conditions include a temperature of about 100 to about 250° C., a pressure of about 50 to about 1000 psig, and a WHSV of about 0.1 to about 100.
More preferably, said conversion conditions include a temperature of about 120 to about 200° C., a pressure of about 200 to about 500 psig, and a WHSV of about 0.5 to about 5.
In a further aspect, the invention resides in a process for the selective production of meta-diisopropylbenzene, said process comprising the steps of:
(a) alkylating benzene with propylene under alkylation conditions in the presence of a solid alkylation catalyst to produce an alkylation product comprising unr
Brown Stephen H.
Bryan Francis S.
Cheng Jane C.
Smith Charles Morris
Weber William A.
Dang Thuan D.
ExxonMobil Chemical Patents Inc.
Tyus Darryl M.
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