Separation of Linear and Branched Paraffins by Adsorption Processes for Gasoline Octane Number Improvement

Separation of hydrocarbons by degree of branching is a very important issue in the development of suitable technologies for enhancing octane number in gasoline fuels. This separation is usually performed by adsorption processes using molecular sieves; hence, a review of these technologies is on demand. This review is devoted to the experimental results on the separation of branched and non-branched C4-C10 hydrocarbons presented in gasoline by means of molecular sieve materials. Experimental gas and liquid phase studies using adsorbents like silicalite, ZSM-5, beta and Y zeolites, ZSM-22, ZSM-23, mordenite, carbon molecular sieves, metal organic frameworks and other hybrids materials are presented. Separation capabilities in gas and liquid phase experiments on single and multiple hydrocarbon mixtures for several adsorbents were analyzed in order to reach a conclusion regarding the use of this type of materials on a commercial procedure. Nevertheless, according to this research from the vast array of materials tested, only the following adsorbents have been included in patented procedures: ZSM-5, ZSM-11, ZSM-23, NU-85, NU-86, NU-87, SSZ-25, SSZ-37, MCM- 22, ERB-1, ITQ-1, PSH-3 and a PVDC derived CMS. The reason behind this lack of advancement may relay on the need of a coupled state of the art isomerization process for the C5-C10 hydrocarbon feeds, and in the design of a material with high adsorption capacity, high selectivity, and high regeneration properties, capable of enduring the complexity of a real feed separation process.