Chemistry of hydrocarbon compounds – Purification – separation – or recovery
Patent
1995-04-14
1997-02-11
Myers, Helane
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
208347, 208350, 208353, 208358, C07C 700
Patent
active
056022930
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Process for separating a feedstock stream essentially consisting of hydrogen, methane and C.sub.3 /C.sub.4 -hydrocarbons.
The invention relates to a process for separating a feedstock stream essentially consisting of hydrogen, methane and C.sub.3 /C.sub.4 -hydrocarbons, which first passes through a pretreatment, such as, e.g., dehydrogenation, after which the feedstock stream undergoes an at least one-stage partial condensation and separation into a C.sub.3 /C.sub.4 -hydrocarbon-rich fraction and into an H.sub.2 /CH.sub.4 fraction, after which a partial stream of the H.sub.2 /CH.sub.4 fraction is mixed in the not yet pretreated feedstock stream.
Processes for separating a feedstock stream essentially consisting of hydrogen, methane and C.sub.3 /C.sub.4 -hydrocarbons are used, e.g., in cryogenic separation, downstream to a dehydrogenation of isobutane to isobutene, of the product stream derived from the dehydrogenation reactor. The dehydrogenation of isobutane to isobutene plays an important role above all in the production of MTBE (methyl-tert-butyl ether), since isobutene and methanol are needed for the production of MTBE. Based on increasingly stiffened exhaust gas regulations for motor vehicles, the use of MTBE, which is used as octane number improver for automotive fuels, will increase in subsequent years. But while methanol is available in sufficient amounts, a considerable deficiency of isobutene exists.
The article "Cryogenic Olefins Recovery from Dehydrogenation Reactor Effluents" by Dr. Heinz C. Bauer (presented at the AIChE Symposium on Cryogenic Gas Processing, 1992 Spring National Meeting, Mar 29-Apr. 2, 1992) provides an overview of the process possibilities for recovering C.sub.3 /C.sub.4 hydrocarbon-rich product fractions available in the prior art. In this case, especially FIG. 13 shows a process for separating a feedstock stream essentially consisting of hydrogen, methane and C.sub.4 -hydrocarbons, in which a part of the recovered gas mixture, consisting of hydrogen and methane, is drawn off from the unit (net fuel gas) and a part is recycled into the dehydrogenation reactor (recycle gas). This recycling of a part of the gas mixture into the dehydrogenation reactor takes place to reduce an undesirable carbon-black formation in it. But this succeeds only incompletely.
According to the invention, it has now been determined that the undesirable carbon-black formation can be better suppressed the higher the hydrogen portion is in the stream recycled into the dehydrogenation reactor. Additional substances, such as, e.g., methane, represent, as the latest studies on which the invention is based have shown, only an unnecessary impurity which both blocks the capacity and worsens the economic efficiency of the process.
The purpose and object of this invention is to indicate a process in which, among others, an H.sub.2 -rich gas stream is recycled into the dehydrogenation and a gas stream containing components to be considered as inert impurities for the process is recovered.
This is achieved according to the invention in that the H.sub.2 /CH.sub.4 gas fraction drawn off from the first separator is divided into two partial streams, and the first partial stream together with the liquid fraction of the first separator is fed to a second separator after partial condensation, the C.sub.3 /C.sub.4 -hydrocarbon-rich liquid fraction, drawn off at the bottom of the second separator, together with the second partial stream of the H.sub.2 /CH.sub.4 gas fraction from the first separator, is conveyed to a stripping column, in that an H.sub.2 -rich gas fraction with high purity is drawn off at the top of the second separator, and after heating in the heat exchange with process streams to be cooled, is mixed with the feedstock stream before its pretreatment and in that a C.sub.3 /C.sub.4 -hydrocarbon-rich product fraction is drawn off at the bottom of the stripping column and an H.sub.2 -rich gas fraction with less high purity is drawn off at the top of the stripping column.
By adding the liquid bott
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Dr. Heinz C. Bauer, "Cryogenic Olefins Recovery from Dehydrogenation. . .", AIChE Symposium on Cryogenic Gas Processing . . . , Mar. 29-Apr. 2, 1992.
Linde Aktiengesellschaft
Myers Helane
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