麻豆传媒

Pushing the limits of selectivity.

In the early days of EO production, the typical start-of-cycle selectivity for the conversion of ethylene to EO by EO catalysts ranged from 68 to 70%. Shell innovations in 1971 increased catalyst selectivity to 80% which was interpreted to be its theoretical limits by industry experts. Shell continues to prove them wrong. In 1986, Shell made a discovery in EO catalyst technology that significantly changed the industry. As a result, it was able to offer new catalysts to the market: High Selectivity (HS) catalysts. This discovery increased initial selectivity values by more than six percentage points to enable many operators to achieve start-of-cycle selectivity values of 86% or greater. The impact of this selectivity increase was huge, as it could save customers millions of dollars in ethylene feedstock costs.

Improving Performance with two Ethylene Oxide/Ethylene Glycol Process Technologies

Shell Catalysts & Technologies is the market鈥檚 leading EO/EG process licensor and EO catalyst producer, and a pioneer in the industry. For more than 50 years, we have led the industry in improving the performance and lifespan of EO catalysts. Over 50% of the world鈥檚 current EO production is manufactured using a Shell EO catalyst.

Using Shell EO/EG technology, refiners and petrochemical producers can:

• Optimise technology configuration to meet local market conditions
• Achieve a fast and smooth start-up
  
• Minimise the production of heavy-glycol by-products if desired
  

Two versions of the Shell Catalysts & Technologies EO/EG process are licensed:

• the Shell MASTER process, which is based on catalyst conversion of ethylene to EO and thermal conversion of EO to EG; and
• the Shell OMEGA process, which is based on catalyst conversion of both ethylene to EO and EO to EG.
  

Both the Shell MASTER process and the Shell OMEGA process are based on and optimised around the use of state-of-the-art Shell EO catalysts with high selectivity and high stability that has enabled many operators to achieve at least three years of operation between catalyst changes at an average catalyst selectivity of about 90%.

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. After plant start-up, Shell Catalysts & Technologies will continue to provide operational support. Process design studies relating to plant modifications or de-bottlenecking can also be accommodated.

Enhancing the EO/EG Manufacturing Process.

Producing EO over a catalyst is the first step in the overall EO/EG manufacturing process. In the reaction section, EO is produced by catalysed, direct partial oxidation of ethylene. Additionally, a portion of the ethylene fully oxidises to form CO₂ and water. These reactions take place in an isothermal (tubular) reactor at temperatures of 230鈥�270掳C. The reaction is moderated/optimised using an organic chloride. EO is recovered from the reactor product gas by absorption in water. Co-produced CO₂ and water are removed, and, after the addition of fresh ethylene and oxygen, the gas mixture is returned to the EO reactor as feed. The EO鈥搘ater mixture can be routed to a purification section for recovery of high-purity EO and/or to a reaction section where EO and water are converted into glycols.

In the standard thermal glycol reaction process, EO and water are reacted at an elevated temperature (about 200掳C) and pressure without catalyst. This process typically yields about 90鈥�92% monoethylene glycol (MEG) and 8鈥�10% heavier glycol products, mainly diethylene glycol (DEG) and triethylene glycol (TEG). The proportion of the higher glycols is limited by using excess water to minimise the reaction between the EO and glycols. The resultant water鈥揼lycol mixture from the reactor is then fed to multiple evaporators where the excess water is recovered and largely recycled. Finally, the water-free glycol mixture is separated by distillation into MEG and the higher glycols.

A more modern technology is to react EO with CO₂ to form ethylene carbonate (EC) and subsequently react the EC with water to form MEG, both reactions being catalysed. In this two-step process, most of the MEG forms in an EO-free environment, which minimises the co-production of heavier glycols and results in a MEG yield of more than 99%.