Advances in methanol synthesis
Catalysts with higher and more stable activity enable cost savings and boost output in methanol production
Terry Fitzpatrick and Tom Hicks
Johnson Matthey Catalysts
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For many years, methanol has been used primarily as a chemical intermediate in manufacturing plastics and resins, then more recently in the manufacture of methyl tertiary butyl ether (MTBE) for use as a lead anti-knock replacement and octane enhancer, allowing a methanol derivative to enter the transportation fuel chain in a significant way for the first time. However, now methanol is being seen as a product that can be introduced directly into the gasoline pool by blending, allowing indigenous resources to be used and providing a diversity of supply that can help to reduce dependence on crude oil and attempt to break the cycle of apparently ever-
escalating oil prices.
China has introduced a national M85 standard that sees gasoline blended with 85% methanol, which has been manufactured using China’s cheap and abundant supplies of coal, helping to reduce its dependence on expensive imported oil.
In the US, there is considerable support for the Open Fuel Standard Act, which, if passed, would call for car manufacturers to introduce flexible fuel vehicles that can run on methanol/ethanol/gasoline mixtures. Currently, there is little methanol production left in North America, but the development of shale gas is set to reduce natural gas prices significantly in North America. And, like China, the US has abundant coal reserves, which, through methanol, could be used to displace oil imported from abroad.
In this article, we will look at methanol synthesis catalysts and discuss the various changes that have occurred in the Katalco range of catalysts against the backdrop of changing industry requirements.
ICI initiated work on catalysts for methanol synthesis in the 1920s, when the only commercial process operated at high pressure. Following early research on copper-zinc catalysts, ICI announced the Low Pressure Methanol (LPM) process in 1963 and the first single-train production unit started operation in 1966.
JM Catalysts has recently developed a new generation of copper zinc methanol synthesis catalysts called Katalco Apico. This extends the performance of the Katalco 51 series catalysts — an improvement that is a step change in methanol synthesis catalysis.
Methanol synthesis catalysts
Since the initial development of the first copper-zinc low-pressure methanol synthesis catalyst, Katalco 51-1, continuing development programmes have improved performance in terms of activity, by-products production, strength, shrinkage and overall life. The original catalyst was designed for application in the multi-bed ICI Quench lozenge converter, and an early variant, Katalco 51-2, quickly became the industry standard. As additional technologies were developed, different types of converter were used, the most noteworthy being gas-cooled and steam-raising in both axial and radial flow configurations. These often impose different requirements on the catalyst, so JM Catalysts has developed a range of synthesis catalysts.
It is worth considering the various changes that have occurred in Katalco catalysts against the backdrop of changing industry requirements. These changes do not come from any one aspect of the catalyst. The enhancements have been generated by identifying and understanding the role of the key components in the formulation and the catalyst manufacturing process itself, as well as improvements in manufacturing control.
The methanol synthesis reaction is an example of a structure insensitive catalytic reaction — one in which the activity is wholly dependent on the total exposed copper area and not affected by the structure of the crystallites. Figure 2 illustrates this direct relationship between activity and copper surface area for catalyst operating under industrial conditions.
This relationship led to suggestions that maximum activity would be achieved with the highest CuO content in the fresh formulation, but this ignored the impact of formulation. As Figure 3 shows, variations in the CuO:Al2O3 ratio have a marked effect on the relative activity, as shown in accelerated life tests.
High initial activity, while important, is not paramount, as the effective useful life of the catalyst will be governed by its stability with time, so the formulation must also stabilise the copper surface area under the process conditions to which it is exposed. Thermal sintering is a key mechanism for synthesis catalyst deactivation with operation at temperatures as high as 315°C, depending on reactor type. Commonly found poisons such as sulphur and, in some cases, iron and nickel carbonyls brought into the loop with fresh syngas also contribute to deactivation or die off. Thus, key formulation requirements are stabilisation of the copper surface area and self-guarding against poisons.
One of the major contributors to a significantly increased in-service activity was the incorporation of magnesia (MgO) into the formulation during the early 1990s. This gave rise to Katalco 51-7 and has been incorporated in subsequent variants Katalco 51-8 and Katalco 51-9. The benefit from incorporating MgO is evident from Figure 4, and the significant improvement relative to Katalco 51-2 in terms of both initial and final activities is illustrated in Figure 5.
Activity testing is a specialised technique comparing aged activities to the catalyst Katalco 51-2. Ageing is reliably simulated by deactivation in a controlled and reproducible manner using elevated temperatures and pressure plus a representative synthesis gas mixture, before measuring activity under standard conditions. A typical test regime measures the activity after 144 hours on-line, representing approximately three months in an operating methanol plant. The results have been validated over the years using data from operating charges in plants and side-stream reactors on our own plants.
Activities are regularly compared with the leading competitive offerings, and the most recent comparison in Figure 6 clearly shows the relative beneficial performance of Katalco 51-9S. The higher and, more critically, stable activity allows operation at lower temperatures, favouring the reaction thermodynamics and loop carbon efficiency, minimising thermal sintering and giving benefits in increased methanol output and reduced by-product formation. The reduced rate of activity loss translates into a longer period of operation between catalyst changes.
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