Is it feasible to use molecular sieves as adsorbents to remove gums from gasoline?
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Molecular sieves, acting as adsorbents, absorb the gums and unsaturated olefins in gasoline, thereby improving its oxidation stability. I wonder if this approach is feasible? So, what is the method for regenerating such molecular sieve adsorbents, and is it easy to implement?
It is feasible, but the losses are very large; if silica gel is used for adsorption, 40–50% of the gasoline components will be lost, and the octane rating of the gasoline will drop significantly.
You can try an activated carbon adsorption test, or a bentonite purification test; it might be useful. Using molecular sieves might be a bit more expensive! But you can try it out! Compare several methods!
White clay purification can be tried, as the loss resulting from white clay purification is relatively small.
If adsorption is used, how is the regeneration of the adsorbent achieved? If white clay adsorption is used, can the used white clay be regenerated online? If activated carbon is used, how is regeneration achieved? This post was last edited by yyleyy on 2008-1-24 09:16]
After using activated carbon for adsorption, the used activated carbon can be regenerated, but the regeneration results in a high loss rate; approximately 20% of the activated carbon is lost. I’m not very familiar with other adsorption methods. In my opinion, although the adsorption method is theoretically feasible, its practical applicability is limited. I believe this is mainly due to two reasons: 1) The components of gums in gasoline are too diverse, making it impossible to remove them completely; as a result, the quality improvement is only temporary. 2) These physical adsorption methods rely on differences in molecular size for adsorption, which results in poor selectivity
We used white clay to adsorb olefins, and the results were fairly good. Normally, the white clay is not regenerated, so it needs to be replaced every three or four months. If the olefin content is relatively high, hydrogenation can be considered. Adsorption by gelatin has not been studied; I think among adsorbents such as activated carbon, activated alumina, and clay, there should be one suitable for this purpose. Molecular sieves generally have very small pores, around 20A or less; if used to adsorb gums, they are likely to become deactivated quite quickly. All of the above are my own deductions; I hope professionals in this field can provide the original poster with professional explanations and suggestions.
The pore size of 13X molecular sieve is 10 Å, allowing it to effectively adsorb molecules with polar groups whose pore size is less than 10 Å; therefore, adsorbing alkenes and unsaturated alkenes is certainly no problem. As for the gums in gasoline, it depends on whether their molecular diameter is less than 10 Å and whether they contain polar functional groups. If it is less than 10A and has polar groups, it should be able to be adsorbed. As for activation, it is easy to achieve using molecular sieves for gas-phase adsorption. That is, medium-low pressure adsorption is used, along with desorption at atmospheric pressure through heating. It can be achieved then. In the case of liquid-phase adsorption, it is relatively difficult to regenerate molecular sieves, mainly because the required equipment is quite complex.
The losses associated with purification using adsorption methods are too high
Using adsorption is feasible and highly effective, but the losses are too great, making it uneconomical. Problems of this kind generally occur only in local refineries; they can be resolved by using acid-base washing. It is best to use dilute phosphoric acid at a concentration of 15–20% (sulfuric acid of the same concentration can also be used), with the amount of acid added being 0.5–2% (depending on the concentration of gums present). After washing, an alkaline solution at a concentration of 12% is used for further cleaning. The amount of gasoline lost is roughly equal to the amount of acid used, and the cleaning effect is very good.