Is there a process for separating alkanes and olefins?
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Hello, esteemed colleagues. I would like to know about the processes for separating alkanes and olefins in fields such as oil refining, ethylene production, and coal chemical industry What’s the point?
To obtain the desired product, there is of course a separation process for alkanes and olefins, such as the production of ethylene and propylene.
Thank you for your advice. I have one more question: what is done with the alkanes such as ethane and propane that are separated from the ethylene plant? Was it burned or returned to the device? Are there any downstream applications as well?
Generally, ethane and propane are cracked in a cracking furnace
Thank you, I have a few more questions. 1. What happens to methane? 2. What happens to C4+? 3. You said that ethane and propane are generally cracked in cracking furnaces; I wonder what proportion this ‘generally’ actually accounts for? Are there any other uses?
Methane is used as the fuel gas; after mixing with C4 to achieve clear separation, it is sent to the C4 unit. C5-C9 are used as feedstock for hydroprocessing of pyrolysis gasoline, followed by C5 extraction and C8 extraction, with the remaining portion serving as the pyrolysis gasoline product. Generally, it’s the vast majority. Some devices may use these ethane and propane to separate the exhaust gases from other devices, for the absorption of exhaust oil, but in the end they still return to the gas furnace.
So, in the end, ethane and propane end up going to the same place; therefore, there’s actually no need to separate them? If I remove methane first and then separate ethylene and propylene from the pyrolysis gas, then I just need to separate C5–C9 and C4 from the pyrolysis gas, right?
Is it not necessary to separate ethane and propane? Theoretically, it can be understood in this way: they are all returned to the propylene cracking furnace ； But in the actual process, carbon dioxide and carbon trioxide are separated as early as in the deethanizer ； Ethylene is then separated in the carbon dioxide separation tower, while propylene is separated in the carbon three separation tower.
There is another question: what considerations underlie pre-deethanization or pre-depropanization? In what situations is the pre-deethanization process preferable, and in what situations is the pre-depropanization process preferable?
What if I don’t need to deethanize? I first remove propane, then methane, leaving only C2 and C3. After removing alkynes, I directly remove olefins; through distillation, ethylene and propylene are separated. Ethane and propane are not separated, and it is easier to separate ethylene and propylene than ethane and ethylene, or propane and propylene. Would such a process save energy? Do you think it has research value?
You are referring to the absorption or extraction process. The ethylene process has been around for nearly a century, and everyone has tried to use these processes. In large-scale ethylene plants, the loss of ethylene and propylene due to cryogenic effects is minimal. For large-scale installations, the requirements regarding recovery rates are much higher than those for smaller installations; as for energy consumption, there is a balance point in relation to the recovery rates. The reason why all patent holders choose the cryogenic separation process for plants producing millions of tons of ethylene is that this equilibrium point shows us that cryogenic separation is more cost-effective.