Patent Application
20170239614
1. Field of the Disclosure
This application relates to systems and methods for enhancing recovery of olefins from methanol to olefin processes. This application particularly relates to such processes where the use of propane in the process is mitigated or even eliminated.
2. Description of the Related Art
Olefins are typically produced by converting a hydrocarbon feed at a high temperature to provide a hydrocarbon mixture containing various alkane, alkene, and alkyne hydrocarbons. The hydrocarbon mixture is then fractionated using a series of distillation columns, fractionation columns, compressors, and refrigeration systems to cool, condense, and separate the various hydrocarbon products. In one method of recovering light hydrocarbons, propane is used to absorb light olefins such as ethylene and propylene, and then recycled after separation of the olefin products.
In one aspect, the invention is a method for recovering light olefins from a methanol to olefin process stream including using an absorption demethanizer unit, wherein the use of propane as an absorbent is reduced or even eliminated by employing C3 and C4 and heavier compounds and mixtures of C3 and C4 and heavier compounds as the absorbent. By employing the demethanizer unit and using less or even no propane, the capital and operating expenditures for the C3 splitting column is greatly reduced offering a competitive advantage to conventional methods.
It should be understood that examples of certain features of the disclosure have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will in some cases form the subject of the claims appended thereto.
For detailed understanding of the present disclosure, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:
In the practice of the method of the application, light olefins are recovered from the effluent of a methanol to olefin process reactor. In such a method, the effluent, after initial treatment to dry and remove undesirable components, becomes a process stream rich in olefins which is then introduced into a demethanizer. The demethanizer employs an absorbent including at least one members selected from the group consisting of C3 hydrocarbons, C3+ hydrocarbons, C4 hydrocarbons, C4+ hydrocarbons, and combinations thereof, with the caveat that when the absorbent is exclusively C3 hydrocarbons, it includes other C3 compounds besides propane.
Absorbents useful with the method of the application include, but are not limited to propylene, one or more butanes, one or more butenes, one or more pentanes, one or more pentenes, and the like. Propane may be used as long as it is not the sole absorbent.
In one aspect, the invention is a method for recovering light olefins from a methanol to olefin process stream including using an absorption demethanizer unit, wherein the use of propane as an absorbent is reduced or even eliminated by employing C3 and C4 and heavier compounds and mixtures of C3 and C4 and heavier compounds as the absorbent. By employing the demethanizer unit and using less or even no propane, the capital and operating expenditures for the C3 splitting column is greatly reduced offering a competitive advantage to conventional methods.
Referring to
The light olefins containing stream enters the demethanizer at a suitable point in the system to effect the desired contact with the C3, C4, and heavier hydrocarbon absorbent fed via flow line 104. For example, the absorbent stream may be fed to the demethanizer at a point above the inlet for stream 102, such that the hydrocarbon solvent flow is countercurrent to the methane, i.e., the solvent flows down the demethanizer to contact the light olefin containing stream counter currently. As the absorbent traverses down the column, the light olefins are absorbed by the absorbent.
The hydrocarbon absorbent and the absorbed light olefins may be recovered from the column as a bottoms fraction via flow line 108. Methane may be recovered from the demethanizer as an overheads fraction via flow line 106. In some embodiments, at least a portion of the overheads fraction may be returned to the demethanizer as a reflux via flow line 112.
In at least some embodiments of the methods of the application, the bottoms fraction will be further treated (not shown in
By employing the method of the application, the amount of propane used to separate the light olefins from the reactor feed is reduced. Since the C3 fraction includes propylene, a desirable product of methanol to olefin conversion, then reduction of the amount of propane used in the process allows for the reduction in size of the C3 splitter. In embodiments, the amount of propane absorbent can make up less than 50%, 25%, 10%, 5%, or 1% of the total amount of absorbent. In embodiments, no propane absorbent is used. This can be a significant capital expenditure savings during construction.
Taking this a step further, the operation, needing less cryogenic distillation to separate and then recycle propane, can then be operated with a savings of energy. These savings in capital and then operational expenses provides for a substantial competitive advantage over a conventional process.
While the embodiment described above is one including building a new unit, it should be appreciated that the demethanizer may be retrofitted into an existing unit. In an alternative embodiment, a demethanizer from a separate process may be repurposed to do the above described separation and then the effluent returned to an otherwise conventional unit for further processing.
Turning to
Turning to
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
