Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce aromatic
Reexamination Certificate
2000-07-25
2002-01-15
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce aromatic
C585S315000, C585S316000, C585S313000, C585S312000, C585S314000, C585S310000, C585S319000, C585S320000, C585S449000, C585S450000, C585S475000, C585S467000
Reexamination Certificate
active
06339179
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 substrate hydrocarbon.
BACKGROUND OF THE INVENTION
The alkylation of aromatic substrates 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 substrate per olefin increases, currently available catalysts typically exhibit an improved selectivity to the monoalkyl aromatic. But even at a high molar ratio of aromatic substrate 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 substrate 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 substrate from the effluents of the alkylation and transalkylation reaction zones. Alkylation reaction zones generally operate at a molar ratio of aromatic substrate per alkylation agent that is at least 1:1 in order to help 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 help 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 substrate, 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 substrate.
Prior art combination processes lessen the great expense incurred in removing and recycling the unreacted aromatic substrate contained in the alkylation and transalkylation reaction zone effluents by three methods. One method is to pass the alkylation effluent stream and the transalkylation effluent stream to a single, common product recovery facility, in which the same distillation columns remove unreacted aromatic from both effluent streams and recycle unreacted aromatic substrate to both reaction zones. In this method, the respective flows through alkylation and transalkylation can be considered to be in parallel. 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 substrate from the effluent streams remains undiminished.
A second method is to pass the entire transalkylation effluent stream to the alkylation zone and then to pass the alkylation effluent stream to the product recovery facility. In this method, the flow through alkylation and transalkylation can be considered as being in series, with transalkylation upstream of alkylation. This arrangement is sometimes referred to as a “cascaded” flow scheme, with transalkylation leading alkylation. The advantage of this method is that unreacted aromatic substrate in the transalkylation effluent stream is directly used in alkylation without expending energy to separate the aromatic substrate from monoalkyl and polyalkyl aromatics. However, an upset condition or any other disruption in the operation of the transalkylation zone propagates directly to the alkylation zone, which can disrupt or adversely affect alkylation reactions. Moreover, even if the transalkylation zone is operating at optimum transalkylation conditions, its effluent may not be an optimum feed stream for the alkylation zone.
A typical scenario helps illustrate the susceptibility to transalkylation upsets of alkylation zones in a cascaded flow scheme with transalkylation leading alkylation. It is well known that the performance of transalkylation catalysts can be affected by the concentration of water in the transalkylation reactor. An unexpected ingress of an excessive amount of water into the transalkylation reactor can cause the conversion of polyalkyl aromatics to monoalkyl aromatics to drop precipitously, say from 70% to 50%. When this occurs in a commercial combination process, levels of polyalkyl aromatics begin to accumulate within the product recovery facility, and in response operators increase the flow rate of polyalkyl aromatics to the transalkylation reactor by 40%. In a cascaded flow scheme with transalkylation leading alkylation, this necessarily increases the flow rate of transalkylation effluent, and especially of polyalkyl aromatics, to the alkylation reactor by 40%. There, the polyalkyl aromatics tend to be further alkylated by olefin, which produces even more highly alkylated polyalkyl aromatics that must be converted in transalkylation. Thus, passing transalkylation effluent to alkylation propagates the initial upset from transalkylation to alkylation and destabilizes the entire combination process. This compounding and prolongation of the initial disturbance can necessitate reducing alkylation throughput and lead to significant economic losses.
A third method is to pass the entire alkylation effluent stream to the transalkylation zone and then to pass the transalkylation effluent stream to the product recovery facility. Like the second method, the flow through alkylation and transalkylation can be considered as being in series, but in this method alkylation is upstream of transalkylation. This arrangement is sometimes referred to as a “cascaded” flow scheme, with alkylation leading transalkylation. Although this method does not expend energy separating unreacted aromatic substrate from the alkylation effluent stream, passing alkylation effluent to transalkylation significantly decreases the yield of the desired monoalkyl aromatic product.
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 efficiently and economically.
SUMMARY OF THE INVENTION
This invention is an economical and efficient combination process for producing an alkyl aromatic by alkylation and by transalkylation. In this invention, one portion of the transalkylation zone effluent stream passes to the alkylation zone, another portion of the tran
Gajda Gregory J.
Schulz Russell C.
Woodle Guy B.
Zarchy Andrew S.
Dang Thuan D.
Moore Michael A.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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