How exactly does re-refining gasoline in a riser reduce olefins?
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How exactly does re-refining gasoline in a riser reduce olefins? Which products are affected?
Since gasoline fractions are small molecules that are relatively difficult to crack compared to catalytic cracking feedstocks, the feed point for the recycled gasoline is generally located at the lower part of the riser, where it first comes into contact with the regenerator. The olefins in the gasoline are cracked into smaller hydrocarbons such as C3 and C4 compounds, which end up in the liquefied gas fraction; as a result, the olefin content in the gasoline decreases.
The liquefied gas yield increases, the gasoline yield decreases, while the diesel yield increases slightly
In simple terms, it involves reprocessing the olefins in gasoline; these olefins are cracked to produce smaller hydrocarbon molecules (C3, C4), thereby reducing the olefin content in gasoline.
Is it the same principle that applies to reducing gasoline olefins in that riser process? Since the olefins in gasoline crack into smaller hydrocarbons such as C3 and C4, which end up in the liquefied gas fraction, why does the yield of gasoline increase with the use of dual lift pipes? Then what is the principle behind those risers in reducing gasoline sulfur content?
It is likely that the olefins in gasoline undergo further reactions of dehydrogenation to form aromatics; in reality, the amount of olefins decreases while the amount of aromatics increases. Controlling the olefin content is actually a means used by Western countries such as the United States to regulate China through standards; in my opinion, the hazards of aromatics in gasoline are far greater than those of olefins.
Refining gasoline to reduce olefins involves converting some of the olefins in gasoline into smaller oligomeric olefins and isoparaffins through reactions such as decomposition, hydrogen transfer, and isomerization, thereby reducing the amount of olefins in the gasoline. A high gasoline yield from twin riser columns is not inevitable; it occurs only under certain conditions, when a portion of the diesel fraction breaks down and enters the gasoline, thereby increasing the gasoline yield.
Gasoline undergoes the following reactions during upgrading: cracking reactions and aromatic hydrogen transfer isomerization. The former produces light hydrogen, while the latter consumes it. Light hydrogen in gasoline is the easiest to decompose; as a result, its concentration decreases. If the reaction temperature is high, the rate of thermal cracking of gasoline increases, leading to an increase in gas production. So gasoline prices rose first and then fell. Diesel production has declined, with cracking feeding into gasoline. Liquefied gas production is rising. The aromatics in gasoline will increase.