In the petrochemical industry when it comes to the production of synthetic fibers, plastics, and similar materials, a vital process is steam cracking through which important chemicals like propylene and ethylene are produced. In steam cracking, there is the thermal decomposition of ethane, propane, or naphtha (basically hydrocarbon feedstock). This is done at high temperatures for the production of lighter hydrocarbons. However, as a by-product of this process, carbon dioxide is produced. This is not desired as there are several issues that this causes like possible reactions with ethylene. Such reactions cause the formation of unwanted byproducts. Another reason CO2 removal is required is that there could be corrosion caused to equipment or deactivation of the catalyst apart from other types of operational challenges. Due to this, the use of a molecular sieve for CO2 removal is required.
The 5A molecular sieve is used for CO2 removal as it has an affinity towards carbon dioxide due to the selective nature of its properties. This molecular sieve for steam cracking is used because when the cracked gas stream is passed through the 5A molecular sieve bed, the CO2 molecules are the ones that are adsorbed. Other gases like propylene and ethylene, on the other hand, are allowed to pass through. Thus, there is efficient CO2 removal with minimal waste. Of course, the capacity of adsorption can be affected by various factors like pressure, the concentration of the CO2 gas as well as temperature. These molecular sieves are preferred for gas generation because they are effective as well as cost-efficient due to their regenerative capacities. Through the application of heat or the reduction of pressure, the CO2 molecules on the adsorbent can be released and thus, the 5A molecular sieve can be reused for removing CO3 from steam-cracked gas.
The Importance of CO2 Removal from Steam-cracked Gas
CO2 as discussed previously is a component that is commonly found in steam-cracked gas as it is produced during the process of steam cracking that takes place in the petrochemical industry. Though not exactly harmful there are negative effects of the presence of CO2 based on its physical properties. Being acidic when it is dissolved in the water it forms carbonic acid. Due to this, when moisture or water is present the carbonic acid formed could lead to the corrosion of pipelines and equipment. Such corrosion leads to the weakening of infrastructure that causes failures, leaks, and inevitably replacement or costly maintenance.
Apart from corrosion, another problem area is the fouling of heat exchangers and other process equipment. The reaction of CO2 with other gas stream components leads to the formation of solid deposits and scale. These can adhere to the surface of the equipment. The heat transfer efficiency thus, is hampered which in turn leads to drops in pressure. Such equipment would need eventual replacement despite the increased frequency of cleaning. CO2 removal is also required because of the negative effects it has on the quality and purity of a product. This holds especially true for separation processes and catalytic reactions. When CO2 reacts with catalysts it reduces the effectiveness of the latter and this reduces the yield as well as the quality of the product. Thus, the efficiency of the separation process is hampered, and obtaining a pure product becomes more challenging.
How 5A Molecular Sieves Work
The basic principle behind the working of 5A molecular sieve for CO2 removal is in the selective adsorption of molecules on the basis of polarity and size. The pores have uniform size and shape and are able to selectively let molecules up to a certain size enter and adhere while they simultaneously exclude molecules that are larger. This same principle comes into play in the case of molecular sieve for steam cracking where the CO2 molecules are trapped from the gas mixture due to their comparatively small size.
It is the properties of 5A molecular sieve that make them so ideal for the gas separation process. Their pore size for instance is 5 angstroms and thus, larger molecules of oxygen and nitrogen are able to pass through undeterred while the smaller molecules of CO2 are trapped due to the molecular filter that operates on pore size. The high adsorption capacity also serves to increase efficiency while the selectivity ensures minimal adsorption of other components from the gas stream. Furthermore, since they are regenerative 5A molecular sieves are a cost-effective option. The process of regeneration also is simple as either the application of heat or the reduction of pressure can cause the trapped CO2 molecules to desorb.
The Benefits of Using 5A Molecular Sieve for CO2 Removal
Some of the prime benefits of using molecular sieves for steam cracking have already been gone through in terms of their selectivity and cost-effectiveness due to regeneration. They are also found to be energy efficient as compared to other techniques for CO2 removal. While some techniques require more energy expended for the capture of CO2 and the regeneration of the molecular sieves, the absorption and desorption processes that have been discussed above run on comparatively lower energy consumption. This helps in the reduction of operational costs.
Apart from the cost and effectiveness, 5A molecular sieves are a scalable adsorption technology that finds applications in various gas flow volumes and rates. Also, they are industry versatile, for instance, they are used in flue gas treatment as well as natural gas purification apart from the petrochemical industry. On an environmental level since there are no chemicals used in this process of CO2 removal it does not affect the environment or human health. The regeneration process too does not require additional chemicals or reagents. As far as stability is concerned, it exhibits good stability in the long term and durability as well. This reduces replacement and maintenance-related costs. All these factors make the use of 5A molecular sieves for CO2 removal ideal for the long run while at the same time providing quality output at a cost-effective rate.