Sep-2024

Third-generation HPPO technology and its benefits

From car seats to mattresses and refrigerators, products made from polyurethane plastics have become integral to our quality of life. Propylene oxide (PO) is a central precursor for this versatile material.

Dr. Heiko Morell and Dr. Uwe Kuehner
Evonik Catalysts

Article Summary

In fact, PO is one of the most industrially valuable chemical intermediates. Unlike other products in the C3 value chain, such as polypropylene – which is predicted to be in oversupply until at least 2030, worldwide demand for PO is rising steadily.

Indeed, the increasing global need for polyurethane plastics translates to a PO market dynamic that surpasses GDP projection; the compound annual growth rate (CAGR) for PO is forecast at 2.7% over the next decade.

However, conventional production methods for PO have raised concerns around environmental impact and economic cost. Increasingly strict environmental regulations in particular have triggered interest in efficient, emissions-saving solutions.

The ‘Hydrogen Peroxide to Propylene Oxide’ (HPPO) method addresses these concerns, providing a more resource-efficient and sustainable PO production process, particularly when paired with specialty catalysts.

Moreover, HPPO can be applied to both existing and new production facilities, making it an ideal option for businesses looking to expand production, phase out old technology or for those looking to enter the market.

A cleaner process
Conventional PO production technologies can be costly and complex, typically relying on integration with chlor-alkali production. Due to this, they often generate significant volumes of by- or co-products, which can result in unnecessary waste as well as the consumption of valuable resources.

HPPO streamlines PO production by using hydrogen peroxide to synthesise PO directly. Specifically, it uses the catalytic reaction of propylene with hydrogen peroxide to oxidise propylene into PO.

It does so without generating wasteful coupling products – water is the only co-product – resulting in fewer downstream processing units required. Consequently, there are fewer steps, reduced energy consumption, less waste and a smaller carbon footprint. Businesses will also benefit from the fact this method boasts lower costs, including for the original investment, in comparison to conventional methods.

Continuous innovation with a newer catalyst
Developed and licensed by Evonik and thyssenkrupp Uhde, the first commercial HPPO plant was commissioned in 2008. Since then, the technology has been continuously refined, especially through enhancements to the titanium silicalite-1 (TS-1) catalyst: a zeolite where individual silicon atoms have been replaced with titanium atoms. The key element for the catalytic activity is the singular titanium atom in a tetrahedral coordination surrounded hydrophobic silica framework, providing highly efficient adsorption of hydrogen peroxide on the active center.

Custom-made by Evonik for the HPPO process, the catalyst – with its optimised pore size – guarantees a high activity and selectivity, as well as a long service life. The latest generation of TS-1 demonstrates even greater performance and service life, due to an improved meso-pore structure and titania dispersion.

Compared to standard TS-1 catalysts – which lose PO process selectivity as temperature increases – Evonik’s propriety catalyst is more effective and long-lasting. Less dependent on reactor temperature, the selectivity starts at a higher level, losing only a minimal 0.5-1% over operation windows, as seen in Figure 1. The catalyst also has a far lower hydrogen peroxide decomposition tendency, which is stable and low at approximately 1%.

During a pilot plant study of the Evonik catalyst, the deactivation rate was unchanged over multiple operation and regeneration cycles. The methanol regeneration incorporated into the activity always brought the catalyst back to the original activity state. In the first years of operation, only two to three regenerations per year are expected, which are done in situ and without removal of the catalyst or plant turndown. 

Commercial success
Since its introduction, the HPPO process has been successfully implemented at manufacturing facilities around the world.

Evonik and thyssenkrupp Uhde licensed the first HPPO plant in South Korea in 2008; subsequent projects have been completed or initiated in Jishen, China; Zibo City, China; and Tiszaújváros, Hungary. In addition to the economic and environmental benefits of HPPO, these licensees also benefit from the highest standards in terms of safety, supply security, and quality of product. Evonik is focused on long-term relationships that offer continuous catalyst and process improvements and life-long plant support. The company’s hydrogen peroxide production technology is also licensed together with a tailored catalyst; licensees have simultaneously built hydrogen peroxide mega plants to provide the raw material directly on-site.   

With each generation of HPPO technology, improvement in performance is evident. The use of the aforementioned proprietary catalyst system has, today, led to a 2% decrease in propylene consumption and a 7% reduction in hydrogen peroxide consumption. In addition, further energy integration measures have resulted in a 17% reduction in steam consumption for the next generation of HPPO plants.

Notably, economic benefits are also measurable. The significantly lower capital investment costs associated with HPPO in comparison with other PO production methods allow businesses greater flexibility in their investment decisions. When factoring in the savings in feedstock and extended catalyst lifetime, changing to the new generation catalyst in existing HPPO plants can generate over €10 million in savings annually.

Looking ahead to the third generation of HPPO plants, the standards of the existing technology will continue to be raised, allowing further CAPEX and OPEX reductions. Savings in steam alone can amount to more than €5 million annually, on top of the reduction of the corresponding CO2 emissions.

Conclusion
HPPO’s economic and environmental advantages have been proven for more than 16 years. With efficient feedstock consumption and low capital investment, the Evonik-Uhde technology presents an extremely cost-effective option, while its streamlined chemical process and high-performance catalyst aligns with sustainable production concepts and superior product quality. Reducing the environmental impact of such setups – from catalyst level to the entire plant – is particularly relevant as global demand for PO rises amid ever-tightening environmental regulations.

As the call for sustainable technologies grows, the next generation of HPPO plants are establishing themselves as the process of the future.