Towards an ideal reactor concept for the production of ethylene from hydrocarbons

Abstract

Ethylene is the world largest volume organic chemical with a worldwide production of approximately 117 million tonnes per year in about 275 plants. The feedstocks for thermal cracking are hydrocarbons: ethane, LPG, naphtha, gas condensates and gas oil. This paper intends to evaluate alternative processes posed in literature, in particular regarding the reactor section of the process. A fundamental point of view is chosen, concentrating on the ability to create a near-optimum reaction path from hydrocarbon feed to ethylene. The critical reactor aspects are high temperature, to be achieved after a short reaction time, at a low hydrocarbon pressure and instantaneously freezing the composition with a high ethylene content by rapid cooling. The majority of the current ethylene production processes are the result of an evolutionary redesign from earlier existing processes; they enable the addition of a large amount of thermal energy in a short period of time at elevated temperature levels in the range of 600 - 1200°C. In this paper the processes are reviewed from a different point of view, namely: how well do they meet the criteria of an ideal process? An ideal process features a maximum olefin yield, no remains of energy carriers or auxiliary chemicals in the product, minimal ecological impact, minimum energy input per unit product, high availability and low degree of complexity of the reaction section. A wide variety of process concepts is covered: dehydrogenation, direct and indirect heating. These processes are related to one another in terms of compliance with the ideal process criteria. Although none of the reported processes fulfils all ideals, the new combination of the adapted firing furnace with ceramic reactors internals and the shock wave reactor come close to it.