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Ethylene oxide/ethylene glycol (EO/EG) processes
Award-winning technology aims to help meet growing demand
The market for EO, about three-quarters of which is converted to EG, is expected to grow at around 5% per year. In January 2014 there were 127 plants producing over 26 Mt/y of EO equivalents. However, the EO derivatives market is highly competitive, and low-cost producers are best positioned for long-term business strength. As well as low feedstock prices and large plant capacities, the application of best-available technology is also of key importance..
About the technology
Shell Global Solutions works with customers to develop safe, cost-effective designs that are tuned to meet local market conditions and customers’ needs. The organisation is one of the market’s leading EO/EG process licensors.
Moreover, the Shell Group (“Shell”) is a major producer of EO and EG through its production facilities in Canada, China, the Netherlands, Singapore and the USA. CRI Catalyst Company (CRI) is the leading EO catalyst producer and a pioneer in the industry. For more than 50 years, CRI and Shell have led the industry in improving the performance and lifespan of EO catalysts. Over 50% of the world’s current EO production is manufactured using a CRI EO catalyst.
Figure 1: The selective MEG technology, combined with the application of a high-selectivity EO catalyst, results in the lowest ethylene consumption per tonne of MEG ever achieved in the industry. Energy consumption, wastewater production and capital costs are also reduced.
Two versions of the Shell EO/EG process are licensed:
- the Shell MASTER process, which is based on a high-selectivity EO catalyst and thermal conversion of EO to EG; and
- the Shell OMEGA process, which is based on highselectivity EO catalyst and monoethylene glycol (MEG) only technology.
In the Shell MASTER process, EO and water are converted to glycols by thermal hydration in a tubular reactor. This process yields roughly 8–10% diethylene glycol (DEG) and triethylene glycol (TEG). The MEG yield depends on the amount of water used in the reaction. Excess water is removed by multiple-effect evaporation, and the individual glycol products are then recovered and purified by distillation.
In the Shell OMEGA process, EO is first reacted with carbon dioxide to form ethylene carbonate, which is then hydrolysed to MEG and carbon dioxide (Figure 1 overleaf). As EO is not present in the hydrolysis reaction, the co-production of DEG and heavier glycols is negligible. Both processes have the option to co-produce high-purity EO.
Plant design is optimised to leverage state-of-the-art, highselectivity EO catalysts and enables at least three years’ operation between catalyst changes at an average catalyst selectivity of about 90%.
The Shell MASTER process makes use of CRI’s latest high-selectivity EO catalyst that can run for three years at about 90% average selectivity. Longer run lengths can also be accommodated. The process co-produces DEG and TEG. The MEG yield is typically 90–92%, depending on customer requirements.
The Shell OMEGA process also uses CRI high-selectivity EO catalyst, and offers significant advantages compared with conventional processes. For instance, it:
- has a MEG selectivity in excess of 99%, which means that virtually no lower-value DEG or TEG is produced;
- produces superior-quality product;
- uses about 20% less steam at equal EO selectivity; and
- produces 30% less waste water.
In addition, a Shell OMEGA plant costs 10% less to build for the same yield.
Since Shell started licensing its EO/EG technology in 1956, more than 70 Shell-designed EO/EG units were commissioned or are currently under construction.
The Shell OMEGA process was acclaimed in the prestigious IChemE Innovation and Excellence Awards 2008 by winning the Engineering Excellence Award.
As every plant is tailor-made and tuned to customer wishes and local conditions and constraints, capital investment costs will vary from plant to plant. In 2004, the capital costs of a 600-kt/y MEG unit were estimated at $120–160 million for the inside-battery-limits portion, but construction and material prices have increased significantly since. After plant start-up, Shell and CRI will continue to provide operational support. Process design studies relating to plant modifications or debottlenecking can also be accommodated.