(52f) Towards an Ideal Reactor Concept for the Production of Ethylene from Hydrocarbons

Ethylene is the world largest volume organic chemical with a worldwide production of approximately 117 million tonnes per year in about 275 plants. Ethylene manufacturing is dominated by steam cracking. This process has evolved significantly from the end of Word War II until present. The plant size has increased from 10,000 tonne to 1.7 million tonne per year. The feedstocks for thermal cracking are hydrocarbons (C2+) like: ethane, LPG, naphtha's, gas condensates and gas oil. Better ethylene yield, and lower energy consumption are achieved by continuous research and development efforts.

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 (C2+) 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 the ideal process? The features of an ideal process involve 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.

The specific energy requirements of the processes considered are only to a limited extend available in the literature; therefore, these requirements have been systematically determined with Aspen plus and the aid of SPYRO® for an ethylene plant with a fixed ethane feed.

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 steam cracking 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.