Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce aromatic
Reexamination Certificate
2000-02-23
2001-08-28
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce aromatic
C585S449000, C585S467000, C585S475000
Reexamination Certificate
active
06281399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a hydrocarbon conversion process. The invention more specifically relates to the production of alkylaromatic hydrocarbons by the reaction of an acyclic olefinic hydrocarbon with an aromatic feed hydrocarbon.
BACKGROUND OF THE INVENTION
The alkylation of aromatics with olefins to produce monoalkyl aromatics is a well developed art which is practiced commercially in large industrial units. One commercial application of this process is the alkylation of benzene with ethylene to produce ethylbenzene which is subsequently used to produce styrene. Another application is the alkylation of benzene with propylene to form cumene (isopropylbenzene) which is subsequently used in the production of phenol and acetone. Those skilled in the art are therefore familiar with the general design and operation of such alkylation processes.
The performances of alkylation processes for producing monoalkyl aromatics are influenced by the stability and activity of the solid catalyst at the operating conditions of the process. For example, as the molar ratio of aromatic per olefin increases, currently available catalysts typically exhibit an improved selectivity to the monoalkyl aromatic. But even at a high molar ratio of aromatic per olefin, several polyalkyl aromatic by-products such as dialkyl aromatics and trialkyl aromatics accompany monoalkyl aromatic production.
Although the formation of dialkyl and trialkyl aromatics might, at first glance, be viewed as by-products that represent a reduction in the efficient use of the olefin, in fact each can be readily transalkylated with the aromatic using a transalkylation catalyst to produce the monoalkyl aromatic. So-called combination processes combine an alkylation zone with a transalkylation zone in order to maximize monoalkyl aromatic production.
One disadvantage of combination processes is that separate reaction zones for alkylation and for transalkylation duplicate costly equipment. Each reaction zone requires what amounts to its own reaction train, including separate and independent reaction vessels, heaters, heat exchangers, piping, and instrumentation.
Another disadvantage of combination processes is the great expense associated with recovering and recycling unreacted aromatic from the effluents of the alkylation and transalkylation reaction zones. Alkylation reaction zones generally operate at a molar ratio of aromatic per alkylation agent that is at least 1:1 in order to ensure a high selectivity toward the monoalkyl aromatic. Transalkylation reaction zones generally operate at a molar ratio of aromatic per dialkyl aromatic that is much greater than the stoichiometric ratio of 1:1 in order to ensure a high conversion of the dialkyl aromatic to the monoalkyl aromatic. Consequently, the alkylation and transalkylation reaction zone effluents contain a significant quantity of unreacted aromatic, which must be removed in order to obtain the monoalkyl aromatic product and which must be recycled in order to ensure the efficient use of the aromatic.
Prior art combination processes lessen the great expense incurred in removing and recycling the unreacted aromatic contained in the alkylation and transalkylation reaction zone effluents by routing each alkylation and transalkylation effluent stream to a single, common product recovery facility, in which the very same distillation columns remove unreacted aromatic from both effluent streams and recycle unreacted aromatic to both reaction zones. Incidentally, a no less important function of these distillation columns in the prior art is the removal of polyalkyl aromatics other than dialkyl and trialkyl aromatics and of other heavy alkylation and transalkylation by-products such as diphenylalkanes, which are collectively referred to herein as heavies. Although sharing common product equipment in this manner reduces the capital expense of a combination process, the energy requirements for vaporizing and condensing the aromatic from the effluent streams remains undiminished.
Thus, the high utilities expenses of combination processes as well as the costly duplication of reaction zones has given impetus to research with a goal of minimizing energy requirements and of integrating the alkylation and transalkylation zones even further.
SUMMARY OF THE INVENTION
This invention is an economical and efficient combination process for producing an isopropyl aromatic by alkylation and by transalkylation. In this invention, portions of the transalkylation effluent stream pass to two or more alkylation beds of a multibed alkylation reaction zone. In one broad embodiment, this invention places the transalkylation and alkylation reaction zones in series, with polyisopropyl aromatics passing to the transalkylation reaction zone with the aromatic alkylation substrate, which is usually benzene, and with portions of the transalkylation effluent passing to two or more beds in a series flow arrangement in the multibed alkylation reaction zone. The alkylation beds to which portions of the transalkylation effluent pass may, but need not be, consecutive beds in the series of beds, and may or may not include the first bed of the series. This invention decreases the formation of polyisopropyl aromatics, especially diisopropyl aromatics, in the alkylation reaction zone, because polyisopropyl aromatics that are present in the transalkylation effluent and which this invention passes to the alkylation zone tend to inhibit the production of polyisopropyl aromatics in the alkylation reaction zone. Because the alkylation reaction zone makes less polyisopropyl aromatics, the transalkylation reaction zone does not need to convert as many polyisopropyl aromatics, and, therefore, the capital and operating costs associated with recycling the alkylation substrate to the transalkylation reaction zone in a combination alkylation-transalkylation process decrease.
Since some alkylation beds in this invention process only a portion of the flow from the transalkylation effluent, those alkylation beds operate at a decreased space velocity in comparison to alkylation beds in the prior art that process the entire flow from the transalkylation effluent. Alkylation beds that do, not receive the entire flow from the transalkylation reaction zone have a total flow rate that is lower than those alkylation beds that do receive the entire flow. Advantage can be taken of this reduction in space velocity to reduce the amount of catalyst in those beds and/or to adjust the flow of alkylating agent to those beds.
The benefits associated with passing portions of the transalkylation effluent to beds other than the first bed in the series of beds of the alkylation zone can be further increased by introducing the alkylation substrate into beds of the alkylation zone. It is now believed that adding additional quantities of alkylation substrate to the alkylation beds, while passing portions of the transalkylation effluent to alkylation beds other than the first of a series of alkylation beds, can decrease the net formation of heavies such as diphenylpropane and alkylated diphenylpropanes. Significantly, it is believed also that there is a synergistic decrease in the formation of these heavies when particular distributions of transalkylation effluent portions to the alkylation beds are used in cooperation with particular distributions of alkylation substrate portions to the alkylation beds. In particular, fewer heavies tend to form when, in an arrangement of alkylation beds in series, the transalkylation effluent portion(s) directed to the upstream alkylation bed(s) are generally smaller than the transalkylation effluent portion(s) directed to the downstream bed(s) while the alkylation substrate portion(s) directed to the upstream alkylation bed(s) are generally larger than the alkylation substrate portion(s) directed to the downstream bed(s). The benefit of decreased heavies formation can, in some circumstances, outweigh the costs associated with recycling the alkylation substrate that are incurred when alkylation substrate that
Gajda Gregory J.
Schulz Russell C.
Woodle Guy B.
Dang Thuan D.
Griffin Walter D.
Moore Michael A.
Spears, Jr. John F.
Tolomei John G.
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