A model decision-making method

In ethylene oxide production, catalyst choice is often the key to profitable performance. CRI Catalyst Company LP (CRI) has developed modelling tools to help operators factor in issues such as the plant design conditions, the local raw material and utility costs and economics, and the preferred run length when selecting catalysts. A combination of economic and predictive catalyst performance models helps to enhance and simplify the catalyst selection process so that operators have a better chance of making the best choice for their plants.

Many of the world’s ethylene oxide plants were built in the 1960s and 1970s and were designed for catalysts with selectivities of about 70%. The latest plants, in contrast, can accommodate the very best in modern catalyst technology and achieve selectivities of 90–92%. Consequently, older plants may not be able to use the newest catalysts or may favour different types of catalysts, even with updated equipment and processes.

“In the production of ethylene oxide, ethylene, as a raw material, accounts for 75–85% of the total production cost,” explains Ross Storey, Technical Service Engineer, CRI. “So, even a small increase in the selectivity of the catalyst will pay a much bigger dividend than almost anything else a plant operator can do to increase efficiency or trim other costs.

Our modelling approach can even help our customers to make crucial decisions on issues such as optimising the run length or justifying the economics behind changing to a better, and sometimes more expensive, catalyst and optimising the cycle time for any type of catalyst.”

The need for an economic model reflects the industry changes and complex challenges faced by ethylene oxide manufacturers. The cost for ethylene 15 years ago, excluding the Middle East, was about $500/t. Today, plants in some areas of the world pay as much as $1400/t for ethylene while others may pay half that or less. There is a similarly wide range of costs for utilities such as steam.

According to Storey: “The rising cost of feedstock makes catalyst performance an even more important consideration. For a typical plant, a 1% improvement in catalyst selectivity would translate into a $2–3 million per year benefit in ethylene cost savings. However, there are numerous factors to be considered in the drive for the optimisation of catalyst choice and operations.

Optimisation efforts must take account of each plant having its own set-up and requiring a tailored approach to catalyst choice and operations owing to its to maximum operating temperatures and ability to remove by‑products. There is no one-size-fits-all solution for ethylene oxide catalysts.

The drive to optimise is further complicated by volatile metal prices. The cost of silver, which is the primary metal element in ethylene oxide catalysts, has risen steeply on the international metals market. This has direct consequences for plant operators in terms of catalyst fill costs and of the economic calculations they make to decide which catalyst gives best value because the amount of silver, the crucial element, varies for different types of catalyst.

In addition, but no less important, there are the potential environmental benefits to consider when making catalyst choices. Boosting selectivity means less production of carbon dioxide, which is the principal by-product of the process. The drive to cut emissions is extremely important for plant operators in Europe, which has some of the strictest emissions targets.

As a leading catalyst supplier, CRI wants to help its customers assess the operational, economic and environmental factors and so make the right choice for their plants.

Storey explains, “Given the range of issues and the complexity of the interactions between the technical, operational, commercial and environmental factors, it is unsurprising that plant operators can find it difficult to decide which catalyst and which process set-up will be most beneficial. This is where CRI can help by bringing the information together in a detailed economic model. Some plants use our models to cross-check their own economic evaluations; others use it as the primary tool for evaluating their options.”

An effective economic modelling approach is needed because the results can be counter-intuitive. In general, the process industry aims for longer cycles, but the best option for modern plants may be shorter runs at substantially higher performance.

Economic modelling also helps operators to identify and quantify the benefits that may be associated with an up-front investment; for example, it might make a high-cost, high-silver-content catalyst more attractive if it is the clear winner in terms of long-term financial return. The economic model can also be used to help clients decide on the optimal cycle time and when a catalyst change might be necessary.

CRI participated in an economic modelling review for the Productora de Alcoholes Hidratados, CA (PRALCA) plant on the eastern shore of Lake Maracaibo in Santa Rita, Venezuela, which has been using  CRI catalysts since its first catalyst change-out in 1996. The modelling showed that the operator could derive significant economic and operational benefits by changing to a more advanced catalyst and making some process changes to make it possible to use this type of catalyst. The necessary investment has been earmarked for the next catalyst cycle.

Freddy Ortega, Engineering Co-ordinator, PRALCA, explains, “Changing to a more efficient catalyst will help to reduce our carbon dioxide emissions and improve our profitability. The economic model, coupled with catalyst performance models, enabled us to estimate the likely savings and to see how they could be achieved. This justified our investment, both in equipment and in the new catalyst.”

By providing modelling tools for both catalysts and economics, CRI offers operators a comprehensive framework for catalyst selection. This approach can model all known plant conditions for all available catalysts; factor in regional ethylene prices and steam cost differences; and include key cost factors such as ethylene and silver price fluctuations. The result is a process that makes it easier for customers to choose the product that matches their plants and operational objectives.

“There is constant innovation in the development of ethylene oxide catalysts, and the range of options now available means that most operators can find a solution that fits the individual plant configuration and cost structure. The choice is not always as obvious as using the most-selective, longest-running, or the least expensive option. The biggest challenge is making a sound technical and economic analysis that helps to guide plants towards the best solution. More often than not, this leads to more value for the customer and for CRI,” concludes Storey.

For more information, contact Ross Storey.