The process of purifying petroleum products has mainly three steps. The first is to separate hydrocarbons from crude oil into smaller fractions of relative property. The second step is to convert these hydrocarbons into probable reaction products. And the final step is to remove the undesirable compounds from the crude itself. Of these, the purifying step initially involved many complicated and costly systems. With the introduction of molecular sieves, these purification processes have become much easier.
Molecular sieves are a porous substance, available as uniform sized balls and these balls have a high affinity towards the possible impurities in petroleum products, like simple water molecules, carbon dioxide, mercaptans, etc. By allowing the petroleum product under the study to pass over a bed of these molecular sieves, under specific pressure, for a pre-calculated time, we can remove all the contaminants and the final product will be a purer form of petroleum product. Dehydration of the zeolite produces an activated form of regular molecular sieves. These activated zeolites make the purification process much cheaper and reliable and produce lead-free high-quality gasoline. It is interesting to note that these zeolites can be regenerated easily by simply purging them with gas streams. The contaminants once adsorbed by the zeolite sieves will be thus removed. So such regenerated sieves can be reused, and this makes the whole system very cost-effective. The process of adsorbing contaminants and desorbing them can be completely automated, which will reduce direct manual interventions in these processes.
The synthetic zeolites also perform a vital role in the catalysis during the petroleum refining process. Zeolites aid in providing improved quality petroleum products, both as a catalyst as well as an adsorbent in separations processes. The process of cracking is a necessary step because the regular distillation might not be sufficient to remove the contaminants, and the final products of distillation might not be consistent. The use of these zeolite sieves as catalysts will enable better selectivity, yield, life, and cost, compared to the other non-zeolite catalysis processes. It also ensures to eliminate the adverse effects caused by the petroleum refining process in the environment and any complications related to energy requirements.
Hydrocracking: a bed of de-aluminated zeolites will convert the hydrocarbons and the hydrogen gas, to produce both high molecular weight petroleum products to low molecular weight fuels. The hydrocarbon – hydrogen gas mixture is allowed to pass through this bed.
Catalytic cracking: In this process, heat the high boiling hydrocarbon fractions to a much-elevated temperature, under moderate pressure, and bring in contact with the desired catalyst. The final product will be shorter molecules of vapor, which are the broken compounds of long long-chain hydrocarbon liquids. The process is almost similar to thermal cracking, except for the presence of a catalyst, which is zeolite sieves.
Thus, the incorporation of activated molecular sieves helps the cracking process of petroleum refining.
Solvent treating and solvent dewaxing are two other steps involved in the petroleum refining process. The first involves the removal of aromatics, impurities, and naphthenes, whereas the second involves removing wax from the arrangement in any stage of the refining process. It is important to imply desiccant drying for these solvents, and the widely used method is the application of molecular sieves for drying solvents.
Molecular sieves for ethanol dehydration:
To prevent engine knocking and enable drivability, a minimum octane number must be maintained in the gasoline. Ethanol is added to gasoline with a lower octane number. Also, the major portion of ethanol in the world is produced as a petroleum by-product. So this ethanol needs to be dehydrated for safe and better performance. Synthetic sieves are used in the ethanol dehydration process. As already discussed, the porous structure of the ethanol molecular sieve and high affinity towards water molecules will attract these water molecules from the ethanol and will be trapped within the sieve pores. Two parallel beds of sieves are used for the process, where one acts as a desiccant and the other undergoes regeneration. So this arrangement ensures a continuous process with the two interchangeable sieve beds. Other than the attractions like easy installation and operation, improved separation efficiency, lower installation, and maintenance cost involved, and maximum alcohol concentration, the main two advantages of ethanol dehydration process are it eliminates any entertainer requirements and it can handle azeotropic compositions effectively.