THERMODYNAMIC ANALYSIS OF FCC REACTIONS BASED ON FUNCTIONAL GROUPS IN HYDROCARBON MOLECULES AND QUANTUM CHEMISTRY FOR PRODUCTION OF LIGHT OLEFINS

Abstract

The relevance of the article is caused by the growth of lower olefins consumption as valuable petrochemical feedstock and the development of technologies for their production, such as fluid catalytic cracking. The most popular petrochemical products are lower olefins, such as propylene, butylene. Every year, 400 million tons of olefins is produced from different technological ways. About 60 % of the world's crude oil is used in fluid catalytic cracking, with application of this technology 59 % of all olefins is produced globally. In accordance with the analysis of the current state of the oil refining and petrochemical industry, in order to increase the yield of olefins, it is indispensable deeply analyze fluid catalytic cracking process and reactions. The establishment of thermodynamic laws is the first step in the analysis of a chemical process. The main aim of the research is to determine the influence of the structure of hydrocarbon isomers on thermodynamic parameters and probability of reactions with the aim of formation of unsaturated gaseous cracking products. Methods: mathematical calculations based on the methods of functional groups including Constantinou–Gani and Joback and the quantum chemistry method done to analyze thermodynamic parameters such as enthalpy and Gibbs free energy of catalytic cracking reactions at various temperatures; assessment of the effectiveness of the methods was done based on the comparison of the mathematical calculation results with literature data. Results. It was percieved that the influence of the structure of isomers on the thermodynamic laws of reactions is much more significant than the change of temperature of fluid catalytic cracking process. As a result of thermodynamic analysis, it was concluded that cracking such isomers is more preferable to obtain gaseous products: 1) 2,2,3-trimethylbutane for production of propylene; 2) 2-methylhexane, 3-methylhexane and 3-ethylpentane for production of propane and iso-butylene; 3) 1-octene for production of butylene. The above gaseous products are obtained by secondary cracking of hydrocarbons in the gasoline fraction. Thus, it is possible to achieve the maximum process selectivity for olefins by selecting the process conditions (temperature, contact time). It is concluded that the method of functional groups based on Constantinoui–Gani accurately describes the thermodynamic laws of cracking reactions, but at the same time does not consider the transformation of non-aromatic compounds and the effect of variations cis- and trans-configurations in the molecular structure. Thus, in these cases it is recommended to use quantum chemistry methods.

Keywords

• catalytic cracking
• thermodynamics
• isomers
• hydrocarbons
• functional groups
• quantum chemistry