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Liquified Petroleum Gas (LPG) is a very popular energy source. This portable, clean and efficient source of energy is a flammable mixture of hydrocarbon gases. In its initial form, it contains impurities. Molecular sieves are used to remove these impurities from LPG so that it is safe and eco-friendly. In this article, this process is discussed in detail.

Mercaptans

Mercaptans are defined, as organic components of hydrocarbons with sulphur. These compounds are considered as impurities when present in large quantities. They have a stringent smell and are corrosive in nature. Mercaptan is the by-product present in natural gases. These impurities must be removed or reduced in quantity, for better performance and longer life of natural gases, LPG and other liquid hydrocarbons. Unfortunately, the mercaptans cannot be removed from LPG by normal distillation.

Molecular sieves for mercaptan removal

The molecular sieve 13X pellets are found to be the most effective method in removing mercaptans from LPG. Molecular sieves are used to separate molecules of different sizes, within a chemical compound. The type X crystalline foam known as molecular sieve type 13X is sodium-based and has a pore diameter of 10A. Thus, molecules of diameter less than 10A will be trapped within the molecular sieve type 13X desiccants.

The process of mercaptan removal from LPG using molecular sieve beds is very simple. The current of LPG to be processed is allowed to pass through a bed of molecular sieve type 13X pellets. As the gas current passes the sieve bed, the mercaptans present in big volumes from the LPG will be adsorbed by molecular sieve beads. The processed LPG is now free from the corrosive components. This adsorption process happens at ambient temperature. But as a huge amount of mercaptans are adsorbed, the molecular sieve beds may become saturated. Allowing a purge gas to pass through these molecular sieve beds will regenerate the sieve bed. This reactivation process is set at an elevated temperature ranging from 200 °C and 325 °C. There can be an arrangement of two sieve beds, which can conduct the adsorption and desorption processes in parallel, thus ensuring a continuous and more efficient process compared to the split process.

However, a very little quantity of one such mercaptan is allowed along with LPG, to identify any leaks, thus avoiding any kind of accidents. Higher regeneration, improved efficiency, and cost-effectiveness of Molecular sieve type 13X are its highlights.