【Alkylation】Alkylation with sulfuric acid Acid concentration
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This post was last edited by Xiao Gong 1985 on 2016-1-29 at 10:12. Have any of those who have worked with alkyl persulfate encountered a situation where the acid concentration during sampling was 85–86%, yet the oil product still passed the quality checks? What could be the reason for this, given that our operating conditions remain unchanged from before? However, it was later found that the acid hydrocarbon ratio increased (probably because other teams added more acid); the acid hydrocarbon ratio reached 2. I would like to ask whether such a high acid hydrocarbon ratio could be causing the oil to encapsulate the acid, resulting in poor separation of the oil from the acid, and thus leading to a lower acid concentration in the samples analyzed. I hope everyone can help answer this.
The acid content in our plant’s units is not less than 90%, with an acid-to-hydrocarbon ratio of 1:1–1.3:1
Senior, could you send some materials for me to study? Thank you. 1093815908@qq.com
Where does your factory take the acid samples from when obtaining acid? Could you send some information on when your factory starts and stops operations? I think the process of starting and stopping operations here is too simple. 702399514@qq.com
In sulfate-based alkylation, the analysis of sulfuric acid concentration is related to factors such as the sampling point, sample collection and transfer, as well as the analytical testing procedures. Due to the strong water-absorbing property of concentrated sulfuric acid, sampling and sample transfer are affected by the humidity of the environment. This needs to be taken into account.
There is an acid-to-hydrocarbon ratio meter next to the reactor in our plant; the acid is isolated half an hour in advance when it needs to be taken. For startup procedures, reference can be made to the operating procedures of CNOOC Huizhou.
Our factory also obtains acid from the acid-hydrocarbon ratio meter, but it seems that that device can get clogged and stop working properly from time to time; therefore, we sometimes use waste acid to prepare samples.
If the ratio of sulfuric acid to hydrocarbons in the reaction system is too low, insufficient acid is available for forming a continuous phase during dispersion and emulsification; instead, the hydrocarbons become the continuous phase. This results in a decrease in the quality of the alkylated oil and an increase in acid consumption. The acid-to-hydrocarbon ratio commonly used in industry is 1–1.5:1 to ensure that sulfuric acid remains in the continuous phase. Since the thermal conductivity of sulfuric acid is much higher than that of hydrocarbons, using sulfuric acid as the continuous phase allows for more effective dissipation of reaction heat, thereby preventing excessive local overheating that could lead to an increase in side reactions. The acid-to-hydrocarbon ratio should also not be too high, as this will reduce the amount of hydrocarbons fed in, thereby decreasing the plant’s processing capacity. Additionally, an increase in sulfuric acid leads to an increase in the viscosity and density of the reaction mixture, which in turn increases the energy required for mixing.
Additionally, the poster also needs to consider the delay in sampling and analysis
When the acid concentration is below 88%, more side reactions occur, which leads to a higher reaction temperature as well as a rapid decrease in the acid concentration. In the case of an acid concentration of 85%-86% as you mentioned, the actual acid concentration inside the reactor should be higher than this value, but not by much (as it still needs to remain below 90%, and this condition persists for an extended period). This is why the acid-to-hydrocarbon ratio is high. The only solution is to replace a large amount of acid in order to quickly increase the acid concentration.
The 85% acidity level you have might be due to the acid having been exposed to air for an extended period before analysis, which caused it to absorb moisture; if this is indeed the concentration, it’s likely that the oil does not meet the required standards. Additionally, a high acid-to-hydrocarbon ratio results in acid encapsulating oil, rather than oil encapsulating acid.