Advances in methanol synthesis Ctlt wth hgh nd tbl ctvt nbl ct vng nd bt utut n thnl ductn Terry FiTzpaTriCk nd Tom HiCks Johnson Matthey Matthey Catalysts
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or 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 signicant way for the rst 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 everescalating 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 exible 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 signicantly 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
Competitor C o m A p e t i t o r B
JM
Others
Fgu 1 Methano technoogy market shares
methanol synthesis catalysts and discuss the various changes that have occurred in the Katalco range of catalysts against the backdrop of changing industry requirements. mthnl ductn 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 rst 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
Nw thnl bng n duct tht cn b ntducd dctl nt th gln l b blndng
series catalysts — an improvement that is a step change in methanol synthesis catalysis. mthnl nth ctlt Since the initial development of the rst 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 ow congurations. 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
Fgu 2 Variation in synthesis catayst activity with copper surface area
been generated by identifying and be achieved with the highest CuO understanding the role of the key content in the fresh formulation, components in the formulation and but this ignored the impact of the catalyst manufacturing process formulation. As Figure 3 shows, itself, as well as improvements in variations in the CuO:Al2O3 ratio manufacturing control. have a marked effect on the relative activity, as shown in accelCtlt ctvt erated life tests. The methanol synthesis reaction is High initial activity, while imporan example of a structure insensi- tant, is not paramount, as the tive catalytic reaction — one in effective useful life of the catalyst which the activity is wholly will be governed by its stability dependent on the total exposed with time, so the formulation must copper area and not affected by the also stabilise the copper surface structure of the crystallites. Figure 2 area under the process conditions illustrates this direct relationship to which it is exposed. Thermal between activity and copper surface sintering is a key mechanism for area for catalyst operating under synthesis catalyst deactivation with industrial conditions. operation at temperatures as high This relationship led to sugges- as 315°C, depending on reactor tions that maximum activity would type. Commonly found poisons
Optimum ratio
Activity
Al2O3
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 signicantly 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 benet from incorporating MgO is evident from Figure 4, and the signicant improvement relative to Katalco 51-2 in terms of both initial and nal 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 benecial performance of Katalco 51-9S. The higher and, more critically, stable activity allows operation at lower temperatures, favouring the reaction thermodynamics and loop carbon efciency, minimising thermal sintering and giving benets 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.
Fgu 3 The impact of catayst formuation on catayst activity
Ctlt tngth nd hng Declining strength and activity were originally the limiting factors
Fgu 4 Effect of incorporating magnesia on copper surface area
Fgu 5 Kataco 51 series activity enhancement
Fgu 6 Comparison of commercia catayst activities
of the catalysts’ operational life. Due to the high copper content, initial catalyst reduction and development of the copper surface area leads to major changes in the physical structure, which is manifested in terms of shrinkage and reduced strength. Low strength during operation, especially during upset conditions, can lead to physical breakage of the pellets, giving increased pressure drop that reduces efciency as well as affecting gas distribution through the catalyst. High shrinkage also leads to distribution problems and a reduced volume of active copper in the reactor. These properties are critical, for instance, in a steamraising reactor such as the axial ow catalyst-in-tube design, where the catalyst duty is quite arduous both in terms of the volume of material charged and the crushing forces to which the catalyst is exposed during thermal cycling. Initially, in the oxidised state, the catalyst must be strong enough to withstand the rigours of charging into the chosen reactor design without breakage. Too high an initial “as received” strength derived from a high pellet density can be a disadvantage, leading to diffusional limitations within the catalyst, affecting overall activity. Through an understanding of the formulation and manufacturing parameters, Katalco 51-9S has been designed with a high pellet density, giving a much enhanced strength both initially and in operation without adding any diffusion limitations, as shown in Berty reactor tests and commercial experience. The most readily obtainable measure of strength is the mean horizontal crush strength (MHCS), appropriately measured across the weakest pellet dimension. Occasionally, the mean vertical crush strength (MVCS) is reported, but this can be misleading, being an order of magnitude higher in the “as received” state. As a result of improvements to the catalyst formulation and manufacturing process, pressure drop increase is no longer a limiting feature of normal plant operation.
In particular, the introduction of post-pellet treatment to the manufacturing process in 2001 has resulted in catalysts that have much greater reduced strength and as little as 5% shrinkage on reduction. Catalyst lives of four to six years, and occasionally as long as eight years, are commonplace, even in the arduous catalyst-in-tube steamraising duty discussed in the case study below.
Chc f ctlt JM Catalysts currently offers four methanol synthesis catalysts; namely, Katalco 51-8, Katalco 518PPT and Katalco 51-9S and the premium product Katalco Apico. Fgu 7 Activity of Kataco 51-9S Providing a range of catalysts, and not relying on a single universal reaction heat removal systems. each charged with 60m3 of Katalco product, caters for the different These include, but are not limited 51-9S. Experience has shown that methanol synthesis technologies to, the direct quench-cooled adia- with this type of reactor careful and enables a choice of product for batic converter design, the axial initial catalyst charging is essential the specic duty. This is particu- steam-raising catalyst-in-tube to ensure minimum pressure drop larly pertinent in a climate where design or the catalyst-in-shell-side, variation between tubes, to give an feedstocks are changing. Natural gas-cooled design such as the tube- even ow distribution and maxigas has been the principal feed for cooled converter. Furthermore, the mum use of the relatively small synthesis gas generation (account- savings through economies of scale volume of catalyst. The catalyst has ing for ~80% of world methanol that might be accrued from build- been producing record production production); synthesis gas genera- ing world-scale methanol plants can levels of 2600 tpd since May 2005, tion historically has largely been benet from the use of radial ow giving signicant nancial benet. based on pure steam methane converters such as the Davy Process As a result of the enhanced reforming, whereas more recently Technology radial steam-raising performance of the catalyst, an there are circumstances when converter. extended run of four years is combined reforming, which planned. JM Catalysts has provided includes an oxygen-red secondary C tud: Ttn mthnl detailed technical support throughor ATR, has its merits. This Lurgi-designed plant has a out, carrying out frequent Coal gasication is another nameplate capacity of 2500 tpd and performance optimisations. Figure method of syngas generation seeing the synthesis loop comprises two 7 conrms the activity achieved, rapid expansion in the number of parallel steam-raising converters, which is 20% greater than Katalco medium- and large-scale methanol projects in China based on a relatively cheap and plentiful resource, with many more plants likely to appear in the future. The US, Australia, India and Russia also have abundant supplies of coal. In relation to the actual converter type, and without going in to too much detail, the different syngas generating technologies yield different syngas compositions (for instance, CO content), each compo sition yielding different reaction rates over the synthesis catalyst. Consideration of the exothermic synthesis reactions means that some converter designs are better suited than others to the different synthesis gases, by virtue of their Fgu 8 Pressure drop stabiity of Kataco 51-9S with time
activity of Katalco Apico catalyst (see Figure 10). As a direct result of the higher activity and stability with time online, the catalyst can be operated for twice as long as any comparable commercial catalyst, leading to fewer catalyst change-outs. On a 2500 tpd plant currently achieving four years between change-outs, the typical time saved by doubling the catalyst life is about nine-and-a-half days, equivalent to at least 23 750 tonnes of product methanol. This is derived from savings on oxidation of the previous catalyst charge prior to discharge, time to discharge and rell and then reduce the new catalyst charge.
Least by-products
Pre-reduced catalyst
Highest activity
Apico
Strongest product available
slowest deactivation
Fgu 9 Sources of benets to operators
51-8 at end of life. Figure 8 shows the pressure drop has remained stable with time, conrming the high strength retention and resistance to breakage in this duty.
Fewer catalyst change-outs. Simply stated, in existing plants, Katalco Apico will make the most methanol, give the longest life and the fastest start-up possible. For a newly designed plant, it offers the smallest reactor and the highest achievable efciency. The following sections show comparative data for Katalco Apico and the current industry standard Katalco 51-9S. •
Bnt Since ICI rst developed the LPM process, copper-based catalysts have improved in small incremental steps at regular intervals until now. The immediate benets to methanol plant operators are signicant: • Increased production • Lower by-product formation • Faster start-ups using prereduced catalyst
Hght nd t tbl ctlt ctvt Comparative activity tests and projections clearly show the higher
Katalco Apico
Katalco 51-9S
Fgu 10 Enhanced activity of Kataco Apico
B-duct ftn The results of tests shown in Figure 11 conrm an even lower level of higher alcohol and other oxygenate by-products with Katalco Apico at typical operating conditions. The benet is further enhanced by being able to operate the catalyst at the lowest temperature possible due to stable activity. On a 2500 tpd unit, using the current generation of catalysts, 98.5% of the crude methanol coming from the synthesis loop is converted to product methanol. With a 50% reduction in higher alcohol by-products, this gure is increased to 99.15% — an increase of 0.65% in methanol produced. Gt tngth Figure 12 shows the measured insitu radial pellet strength compared with the best currently available product. The 50% increase in operating strength ensures the catalyst is better able to withstand upset conditions without physical breakage. This results in a more stable pressure drop so that efciency and gas distribution are maintained. p-ducd ctlt Katalco Apico catalysts are supplied in the reduced form, which ensures the catalyst has been activated to achieve maximum unit activity. Since there is no shrinkage associated with normal catalyst reduction, this also maximises the
amount of active copper charged. By using a pre-reduced catalyst, there is a typical saving of around 30 hours for a new charge, representing at least 3000 tonnes of product methanol on a 2500 tpd plant. ovll bnt As indicated in the previous sections, the enhanced performance of Katalco Apico leads to benets in many aspects of plant operation. These are summarised in Table 1. The total value of these benets is over $25 million in additional methanol sales (assumed methanol price $200/t). Additional savings related to manning and material costs of shutdown may also be realised. C tud: ktlc pfnc A methanol plant in Asia using a combination of Katalco catalysts in the tubular reformer contracted JM Catalysts to do a specialist reformer survey to check the performance and make recommendations for any possible optimisation. The furnace was found to be in need of balancing and it was also shown that the process gas temperature could be safely increased without compromising tube life. Detailed recommendations on balancing the furnace were implemented on the plant, with a resultant increase of 60 tpd of methanol make worth over $3 million/y.
Fgu 11 Seectivity improvement with Kataco Apico
KATAlCO jM and APICO jM are marks of the johnson Matthey Group of Companies.
T Fttc is Methano Technoogy
Manager within the GTl group of johnson Matthey Cataysts. His work has a particuar emphasis on the deveopment of technoogy and catayst appications for methano chemistry. He oined the catayst business (then ICI) over 20 years ago and has a bacheor’s degree in chemica engineering from Cambridge University, UK. T Hc is a consutant with johnson Matthey Cataysts. He has worked on steam reforming cataysts and technoogy, shift and methano cataysts, acetyene hydrogenation cataysts and ammonia synthesis technoogy for ICI and now johnson Matthey, and has a bacheor’s degree in chemistry from Durham University, UK.
Fgu 12 In-situ radia peet strength of Kataco Apico
otng bnt f ktlc ac Ftu
Pre-reduced catayst Higher, stabe activity Doubed catayst ife 50% ower by-products
Tbl 1
Bnt t t
ext moH, tnn
Faster start-up Additiona MeOH made Eiminated change-out Increased efciency Tota
3000 55 000 23 750 45 000 126 750
