Boosting Catalyst Productivity

For the better part of a century, chemical process industries (CPI) have depended on catalysts to make their processes viable. Current efforts toward process efficiency and environmental innocuousness have placed more demands on catalysts to produce more with less.

Industrial catalyst manufacturers are partners in the effort; they are pursuing several different pathways to maximize their products’ ability to boost output for those who use them. Among the strategies are to find ways to maintain product yields with less catalyst, and to improve catalyst activity without sacrificing selectivity.

There have been several recent examples where new catalysts have helped realize manufacturing advantages. Success has been reached through the use of alternate catalyst materials, new support designs and new manufacturing methodology.

Engineering particle size

Heterogeneous catalyst activity and selectivity are affected strongly by catalyst particle size. One strategy to improve productivity is to find ways to make uniform-sized catalyst particles that are optimally sized to perform the needed reactions. The BASF (Ludwigshafen, Germany; http://www.basf.com) catalyst division is applying that approach in its NanoSelect platform, a commercially viable process for manufacturing metal crystallites of a specific size. The first two products under the NanoSelect umbrella are LF100 and LF200, which are the world’s first lead-free alternatives to Lindlar catalysts. Lindlar catalysts are lead-modified heterogeneous palladium catalysts that, for example, hydrogenate alkynes to selectively produce cis -, rather than trans -alkenes.

The picture show Metal clusters with a narrow size distribution, such as these produced on BASF’s Nanotechnology platform improve activity while reducing metal content. (Photo: BASF).

BASF Catalysts global product technology manager Hans Donkervoort explains that standard heterogeneous catalysts have metal crystallite sizes varying from <1 to 100 nm. The NanoSelect platform is designed to make metal colloids with metal crystallites sized in a very narrow, almost unimodal size range — for example, 7.0±1.5 nm.

“For the LF 100 and 200 catalysts, we are able to produce metal crystallites in a specific narrow range, which allows BASF to achieve the same functionality with the NanoSelect catalyst as that of a Lindlar catalyst,” Donkervoort says. In addition, these catalysts require less palladium metal to achieve the same hydrogenation activity, which leads to significant cost reductions in the hydrogenation process. “Palladium content of Lindlar catalysts is about 5% by weight, while the LF 100 and 200 have around 0.5 or 0.6% palladium by weight,” Donkervoort explains, “but hydrogenation activity levels are similar.”

The BASF LF Series catalysts also eliminate the need for lead. The role of lead in Lindlar-catalyzed reactions is important, but not well understood.

For developing the lead-free hydrogenation catalysts, BASF won a “Green Excellence Award” from Frost & Sullivan (San Antonio, Tex.; http://www.frost.com) in August 2009.

“Feedback from [LF catalyst] users in the market has been good,” Donkervoort says. “Performance is the same [as existing Lindlar catalysts], including selectivity for the cis versus trans double bond.”

The two catalysts constructed on the NanoSelect platform differ in the support material used — in the case of LF 100, the support is activated carbon, and for LF 200, the support is alumina-silicate powder.

BASF’s catalyst division is currently working on producing other catalysts on the NanoSelect platform, including multimetallic systems. The company is also seeking collaborations with university research groups to learn more about the fundamental chemistry of the catalyst systems.

In addition to working on new NanoSelect catalysts, BASF engineers are also developing catalysts that are compatible with other strategies manufacturers may be pursuing toward achieving higher productivity in their processes. Succeeding in doing so could include moving from a batch-production model to continuous production, Donkervoort explains. Companies are looking to downsize their equipment and make more product with smaller process hardware, Donkervoort says, and “it’s up to us to develop catalysts that will be effective” in such a scheme.

Recovering energy from fluegas

Alcoa of Australia (www.alcoa.com.au) has developed a process to recover sensible and latent heat from the fluegas (FG) produced by Bayer alumina calciners, and use the heat to evaporate Bayer spent liquor. Peter Hay, of Alcoa’s Technology Delivery Group, at Alcoa’s Kwinana Refinery, in Western Australia, says the recovered heat can also be applied to seawater desalination. Calcination consumes 25 to 40% of the refinery’s total energy input, and produces large quantities of FG that is generally vented to the atmosphere, says Hay.

Energy is recovered from the FG by progressive cooling. Only sensible heat is recovered between 165°C and the dew point. Below the dew point, the energy recovered is mainly the latent heat of the water condensed. The higher-grade, sensible heat is only about 10% of the practical recoverable energy, considering 50°C to be the heat sink practical limit. Water is recovered after the dew point is reached. Since considerable refining infrastructure is invested to collect and store fresh water — an essential raw material for the Bayer process — any process that can reduce fresh water usage has significant value to the refining operation, says Hays.

The basic components of the heat recovery process (flowsheet) are: fluegas quench to cool the FG to its dew point and to wet and discharge the fugitive dust in the FG; counter-current contacting tower to heat water and cool the FG; induced draft fan to overcome pressure losses in the FG circuit; indirect exhaust FG heater to ensure fluegas buoyancy and dispersion; falling film evaporator, to exchange heat between the heated water in the shell with the spent liquor film flowing inside the tubes thereby evaporating the spent liquor; and indirect heat exchanger, to condense and recover high quality condensate from the evaporated liquor.

For every metric ton of smelting-grade alumina produced, about 0.2 GJ of sensible heat is recovered from FG exit temperatures between 85 and 165°C, and about 0.6 m.t. of water is recovered from FG exit temperatures between 57 and 82°C. Hay and co-inventor Dean Ilievski, also of Alcoa’s Technology Delivery Group, have applied for a patent on the process.