What is the reason for the rapid decline in the concentration of alkylated acids?
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Part of the alkylation feedstock came from the overhead product of the MTBE catalytic distillation column, while the other part was purchased raw material. At that time, the MTBE reactor was not functioning properly, apparently due to catalyst deactivation; the MTBE production was halted the next day. Then the concentration of alkylated acid decreased, resulting in a higher proportion of heavy components in the isooctane product. Simultaneous analysis showed that the sulfide levels in the material taken from the top of the alkylated methanol tower (used as MTBE raw material) and at the bottom of the tower were very high, around 70–150 mg/L. The dehydration process in the dehydrator before the reactor also resulted in high sulfide levels, approximately 300 mg/L (due to limited laboratory facilities, it was not possible to determine the specific composition of these sulfides). Additionally, the concentrated sulfuric acid used for alkylation is acid produced internally by the waste acid treatment unit, whose raw materials contain hydrogen sulfide.
It seems to be caused by the high water content in the raw materials.
The only things that could cause a rapid drop in sulfuric acid concentration are probably water and propylene
Is the MTBE content high in the raw materials? Being too high would also lead to a decrease in acid concentration, right?
Is the hydrogen sulfide level higher than usual? Hydrogen sulfide can also consume acid, or maybe acid has not been replenished in time
The consumption of alcohols and ethers in the raw materials is quite high; additionally, the amount of acid required to process sulfides is also significant – 60 tons of sulfuric acid are needed per ton of sulfides. As for the amount of acid consumed for water treatment, it goes without saying that it is even higher. When encountering such a problem, it is necessary to urgently replace the sulfuric acid, reduce the processing volume, and prevent acid from leaking to the back side; if control becomes impossible, operations must be halted. For reference only!
As for what you said about hydrogen sulfide being generated in the spent acid regeneration unit and affecting the alkylation unit, I don’t quite agree with that.
When the sulfuric acid concentration is below 85, it drops sharply, and in severe cases this can lead to chemical acid leakage
Hydrogen sulfide acid consumption coefficient 12-15